subtree(users/wpcarro): docking briefcase at '24f5a642'

git-subtree-dir: users/wpcarro git-subtree-mainline: 464bbcb15c git-subtree-split: 24f5a642af Change-Id: I6105b3762b79126b3488359c95978cadb3efa789
2021-12-14 01:51:19 +03:00 · 2021-12-14 01:51:19 +03:00 · 019f8fd211
commit 019f8fd211
parent 464bbcb15c 6123e97692
766 changed files with 175420 additions and 0 deletions
--- a/users/wpcarro/scratch/deepmind/part_one/balanced-binary-tree.py
+++ b/users/wpcarro/scratch/deepmind/part_one/balanced-binary-tree.py
@ -0,0 +1,123 @@
+import unittest
+from collections import deque
+
+
+def is_balanced(node):
+    q, seen, ds = deque(), set(), set()
+    q.append((0, node))
+    while q:
+        d, node = q.popleft()
+        l, r = node.left, node.right
+        seen.add(node)
+        if not l and not r:
+            if d not in ds and len(ds) == 2:
+                return False
+            else:
+                ds.add(d)
+        if l and l not in seen:
+            q.append((d + 1, l))
+        if r and r not in seen:
+            q.append((d + 1, r))
+    return max(ds) - min(ds) <= 1
+
+
+# Tests
+class Test(unittest.TestCase):
+    class BinaryTreeNode(object):
+        def __init__(self, value):
+            self.value = value
+            self.left = None
+            self.right = None
+
+        def insert_left(self, value):
+            self.left = Test.BinaryTreeNode(value)
+            return self.left
+
+        def insert_right(self, value):
+            self.right = Test.BinaryTreeNode(value)
+            return self.right
+
+    def test_full_tree(self):
+        tree = Test.BinaryTreeNode(5)
+        left = tree.insert_left(8)
+        right = tree.insert_right(6)
+        left.insert_left(1)
+        left.insert_right(2)
+        right.insert_left(3)
+        right.insert_right(4)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_both_leaves_at_the_same_depth(self):
+        tree = Test.BinaryTreeNode(3)
+        left = tree.insert_left(4)
+        right = tree.insert_right(2)
+        left.insert_left(1)
+        right.insert_right(9)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_leaf_heights_differ_by_one(self):
+        tree = Test.BinaryTreeNode(6)
+        left = tree.insert_left(1)
+        right = tree.insert_right(0)
+        right.insert_right(7)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_leaf_heights_differ_by_two(self):
+        tree = Test.BinaryTreeNode(6)
+        left = tree.insert_left(1)
+        right = tree.insert_right(0)
+        right_right = right.insert_right(7)
+        right_right.insert_right(8)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_three_leaves_total(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(5)
+        right = tree.insert_right(9)
+        right.insert_left(8)
+        right.insert_right(5)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_both_subtrees_superbalanced(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(5)
+        right = tree.insert_right(9)
+        right_left = right.insert_left(8)
+        right.insert_right(5)
+        right_left.insert_left(7)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_both_subtrees_superbalanced_two(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(2)
+        right = tree.insert_right(4)
+        left.insert_left(3)
+        left_right = left.insert_right(7)
+        left_right.insert_right(8)
+        right_right = right.insert_right(5)
+        right_right_right = right_right.insert_right(6)
+        right_right_right.insert_right(9)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_only_one_node(self):
+        tree = Test.BinaryTreeNode(1)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_linked_list_tree(self):
+        tree = Test.BinaryTreeNode(1)
+        right = tree.insert_right(2)
+        right_right = right.insert_right(3)
+        right_right.insert_right(4)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/dijkstra.py
+++ b/users/wpcarro/scratch/deepmind/part_one/dijkstra.py
@ -0,0 +1,26 @@
+# Doing a practice implementation of Dijkstra's algorithm: a priority-first
+# search.
+from heapq import heappush, heappop
+
+
+class Node(object):
+    def __init__(self, value, children):
+        self.value = value
+        self.children = children
+
+
+def shortest_path(a, b):
+    """Return the shortest path from `a` to `b`."""
+    q = []
+    seen = set()
+    heappush((a.value, a, [a]), q)
+
+    while q:
+        d, node, path = heappop(q)
+        if node == b:
+            return path
+        seen.add(node)
+        for child in node.children:
+            if child not in seen:
+                heappush((d + child.value, child, path + [child]), q)
+    raise Exception("Path between nodes A and B does not exist.")
--- a/users/wpcarro/scratch/deepmind/part_one/efficiency.org
+++ b/users/wpcarro/scratch/deepmind/part_one/efficiency.org
@ -0,0 +1,6 @@
+* Sorting
+** Merge:	O(n*log(n))
+** Heap:	O(n*log(n))
+** Insertion:	O(n^2)
+** Quick:	O(n^2)
+** Bubble:	O(n^2)
--- a/users/wpcarro/scratch/deepmind/part_one/find-rotation-point.py
+++ b/users/wpcarro/scratch/deepmind/part_one/find-rotation-point.py
@ -0,0 +1,55 @@
+import unittest
+from math import floor
+
+
+def midpoint(a, b):
+    return a + floor((b - a) / 2)
+
+
+def do_find_rotation_point(a, b, xs):
+    i = midpoint(a, b)
+    count = b - a + 1
+
+    if count == 2:
+        if xs[a] > xs[b]:
+            return b
+        else:
+            return -1
+
+    if i in {a, b}:
+        return i
+
+    if xs[a] < xs[i]:
+        return do_find_rotation_point(i, b, xs)
+    else:
+        return do_find_rotation_point(a, i, xs)
+
+
+def find_rotation_point(xs):
+    return do_find_rotation_point(0, len(xs) - 1, xs)
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_small_list(self):
+        actual = find_rotation_point(['cape', 'cake'])
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_medium_list(self):
+        actual = find_rotation_point(
+            ['grape', 'orange', 'plum', 'radish', 'apple'])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_large_list(self):
+        actual = find_rotation_point([
+            'ptolemaic', 'retrograde', 'supplant', 'undulate', 'xenoepist',
+            'asymptote', 'babka', 'banoffee', 'engender', 'karpatka',
+            'othellolagkage'
+        ])
+        expected = 5
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/inflight-entertainment.py
+++ b/users/wpcarro/scratch/deepmind/part_one/inflight-entertainment.py
@ -0,0 +1,51 @@
+import unittest
+
+
+def can_two_movies_fill_flight(xs, t):
+    seeking = set()
+    for x in xs:
+        if x in seeking:
+            return True
+        else:
+            seeking.add(t - x)
+    return False
+
+
+# Tests
+
+
+class Test(unittest.TestCase):
+    def test_short_flight(self):
+        result = can_two_movies_fill_flight([2, 4], 1)
+        self.assertFalse(result)
+
+    def test_long_flight(self):
+        result = can_two_movies_fill_flight([2, 4], 6)
+        self.assertTrue(result)
+
+    def test_one_movie_half_flight_length(self):
+        result = can_two_movies_fill_flight([3, 8], 6)
+        self.assertFalse(result)
+
+    def test_two_movies_half_flight_length(self):
+        result = can_two_movies_fill_flight([3, 8, 3], 6)
+        self.assertTrue(result)
+
+    def test_lots_of_possible_pairs(self):
+        result = can_two_movies_fill_flight([1, 2, 3, 4, 5, 6], 7)
+        self.assertTrue(result)
+
+    def test_not_using_first_movie(self):
+        result = can_two_movies_fill_flight([4, 3, 2], 5)
+        self.assertTrue(result)
+
+    def test_only_one_movie(self):
+        result = can_two_movies_fill_flight([6], 6)
+        self.assertFalse(result)
+
+    def test_no_movies(self):
+        result = can_two_movies_fill_flight([], 2)
+        self.assertFalse(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/kth-to-last.py
+++ b/users/wpcarro/scratch/deepmind/part_one/kth-to-last.py
@ -0,0 +1,64 @@
+import unittest
+
+
+def kth_to_last_node(k, x):
+    a, b = x, x
+
+    if k == 0:
+        raise Exception('Value of 0 for k is not supported')
+
+    for _ in range(k - 1):
+        if not a.next:
+            raise Exception('Value of {} for k is too large'.format(k))
+        a = a.next
+
+    while a.next:
+        a, b = a.next, b.next
+    return b
+
+
+class Test(unittest.TestCase):
+    class LinkedListNode(object):
+        def __init__(self, value, next=None):
+            self.value = value
+            self.next = next
+
+        def get_values(self):
+            node = self
+            values = []
+            while node is not None:
+                values.append(node.value)
+                node = node.next
+            return values
+
+    def setUp(self):
+        self.fourth = Test.LinkedListNode(4)
+        self.third = Test.LinkedListNode(3, self.fourth)
+        self.second = Test.LinkedListNode(2, self.third)
+        self.first = Test.LinkedListNode(1, self.second)
+
+    def test_first_to_last_node(self):
+        actual = kth_to_last_node(1, self.first)
+        expected = self.fourth
+        self.assertEqual(actual, expected)
+
+    def test_second_to_last_node(self):
+        actual = kth_to_last_node(2, self.first)
+        expected = self.third
+        self.assertEqual(actual, expected)
+
+    def test_first_node(self):
+        actual = kth_to_last_node(4, self.first)
+        expected = self.first
+        self.assertEqual(actual, expected)
+
+    def test_k_greater_than_linked_list_length(self):
+        with self.assertRaises(Exception):
+            kth_to_last_node(5, self.first)
+
+    def test_k_is_zero(self):
+        with self.assertRaises(Exception):
+            kth_to_last_node(0, self.first)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/merging-ranges.py
+++ b/users/wpcarro/scratch/deepmind/part_one/merging-ranges.py
@ -0,0 +1,59 @@
+import unittest
+
+
+def merge_ranges(xs):
+    xs.sort()
+    result = [xs[0]]
+    for curr in xs[1:]:
+        a, z = result[-1]
+        if z >= curr[0]:
+            result[-1] = (a, max(z, curr[1]))
+        else:
+            result.append(curr)
+    return result
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_meetings_overlap(self):
+        actual = merge_ranges([(1, 3), (2, 4)])
+        expected = [(1, 4)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_touch(self):
+        actual = merge_ranges([(5, 6), (6, 8)])
+        expected = [(5, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meeting_contains_other_meeting(self):
+        actual = merge_ranges([(1, 8), (2, 5)])
+        expected = [(1, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_stay_separate(self):
+        actual = merge_ranges([(1, 3), (4, 8)])
+        expected = [(1, 3), (4, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_multiple_merged_meetings(self):
+        actual = merge_ranges([(1, 4), (2, 5), (5, 8)])
+        expected = [(1, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_not_sorted(self):
+        actual = merge_ranges([(5, 8), (1, 4), (6, 8)])
+        expected = [(1, 4), (5, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_one_long_meeting_contains_smaller_meetings(self):
+        actual = merge_ranges([(1, 10), (2, 5), (6, 8), (9, 10), (10, 12)])
+        expected = [(1, 12)]
+        self.assertEqual(actual, expected)
+
+    def test_sample_input(self):
+        actual = merge_ranges([(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)])
+        expected = [(0, 1), (3, 8), (9, 12)]
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/recursive-string-permutations.py
+++ b/users/wpcarro/scratch/deepmind/part_one/recursive-string-permutations.py
@ -0,0 +1,56 @@
+import unittest
+from itertools import permutations
+
+
+class Node(object):
+    def __init__(self, x):
+        self.value = x
+        self.children = []
+
+
+def make_tree(c, xs):
+    root = Node(c)
+    for x in xs:
+        root.children.append(make_tree(x, xs - {x}))
+    return root
+
+
+def get_permutations(xs):
+    xs = set(xs)
+    root = make_tree("", xs)
+    q, perms = [], set()
+    q.append(("", root))
+    while q:
+        c, node = q.pop()
+        if not node.children:
+            perms.add(c)
+        else:
+            for child in node.children:
+                q.append((c + child.value, child))
+    return perms
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_empty_string(self):
+        actual = get_permutations('')
+        expected = set([''])
+        self.assertEqual(actual, expected)
+
+    def test_one_character_string(self):
+        actual = get_permutations('a')
+        expected = set(['a'])
+        self.assertEqual(actual, expected)
+
+    def test_two_character_string(self):
+        actual = get_permutations('ab')
+        expected = set(['ab', 'ba'])
+        self.assertEqual(actual, expected)
+
+    def test_three_character_string(self):
+        actual = get_permutations('abc')
+        expected = set(['abc', 'acb', 'bac', 'bca', 'cab', 'cba'])
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/reverse-linked-list.py
+++ b/users/wpcarro/scratch/deepmind/part_one/reverse-linked-list.py
@ -0,0 +1,74 @@
+import unittest
+
+
+def reverse(node):
+    prev = None
+    next = None
+    curr = node
+
+    while curr:
+        next = curr.next
+        curr.next = prev
+        prev = curr
+        curr = next
+
+    return prev
+
+
+# Tests
+class Test(unittest.TestCase):
+    class LinkedListNode(object):
+        def __init__(self, value, next=None):
+            self.value = value
+            self.next = next
+
+        def get_values(self):
+            node = self
+            values = []
+            while node is not None:
+                values.append(node.value)
+                node = node.next
+            return values
+
+    def test_short_linked_list(self):
+        second = Test.LinkedListNode(2)
+        first = Test.LinkedListNode(1, second)
+
+        result = reverse(first)
+        self.assertIsNotNone(result)
+
+        actual = result.get_values()
+        expected = [2, 1]
+        self.assertEqual(actual, expected)
+
+    def test_long_linked_list(self):
+        sixth = Test.LinkedListNode(6)
+        fifth = Test.LinkedListNode(5, sixth)
+        fourth = Test.LinkedListNode(4, fifth)
+        third = Test.LinkedListNode(3, fourth)
+        second = Test.LinkedListNode(2, third)
+        first = Test.LinkedListNode(1, second)
+
+        result = reverse(first)
+        self.assertIsNotNone(result)
+
+        actual = result.get_values()
+        expected = [6, 5, 4, 3, 2, 1]
+        self.assertEqual(actual, expected)
+
+    def test_one_element_linked_list(self):
+        first = Test.LinkedListNode(1)
+
+        result = reverse(first)
+        self.assertIsNotNone(result)
+
+        actual = result.get_values()
+        expected = [1]
+        self.assertEqual(actual, expected)
+
+    def test_empty_linked_list(self):
+        result = reverse(None)
+        self.assertIsNone(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/stock-price.py
+++ b/users/wpcarro/scratch/deepmind/part_one/stock-price.py
@ -0,0 +1,51 @@
+def get_max_profit(xs):
+    best_profit = xs[1] - xs[0]
+    lowest_buy = xs[0]
+
+    for x in xs[1:]:
+        best_profit = max(best_profit, x - lowest_buy)
+        lowest_buy = min(lowest_buy, x)
+    return best_profit
+
+
+# Tests
+
+import unittest
+
+
+class Test(unittest.TestCase):
+    def test_price_goes_up_then_down(self):
+        actual = get_max_profit([1, 5, 3, 2])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_down_then_up(self):
+        actual = get_max_profit([7, 2, 8, 9])
+        expected = 7
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_up_all_day(self):
+        actual = get_max_profit([1, 6, 7, 9])
+        expected = 8
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_down_all_day(self):
+        actual = get_max_profit([9, 7, 4, 1])
+        expected = -2
+        self.assertEqual(actual, expected)
+
+    def test_price_stays_the_same_all_day(self):
+        actual = get_max_profit([1, 1, 1, 1])
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_error_with_empty_prices(self):
+        with self.assertRaises(Exception):
+            get_max_profit([])
+
+    def test_error_with_one_price(self):
+        with self.assertRaises(Exception):
+            get_max_profit([1])
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_one/which-appears-twice.py
+++ b/users/wpcarro/scratch/deepmind/part_one/which-appears-twice.py
@ -0,0 +1,29 @@
+import unittest
+
+
+def find_repeat(xs):
+    n = max(xs)
+    expected_sum = (n + 1) * n / 2
+    actual_sum = sum(xs)
+    return actual_sum - expected_sum
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_short_list(self):
+        actual = find_repeat([1, 2, 1])
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_medium_list(self):
+        actual = find_repeat([4, 1, 3, 4, 2])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_long_list(self):
+        actual = find_repeat([1, 5, 9, 7, 2, 6, 3, 8, 2, 4])
+        expected = 2
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/.envrc
+++ b/users/wpcarro/scratch/deepmind/part_two/.envrc
@ -0,0 +1,2 @@
+source_up
+use_nix
--- a/users/wpcarro/scratch/deepmind/part_two/balanced-binary-tree.py
+++ b/users/wpcarro/scratch/deepmind/part_two/balanced-binary-tree.py
@ -0,0 +1,126 @@
+import unittest
+from collections import deque
+
+
+# is_balanced :: Node(a) -> Bool
+def is_balanced(node):
+    q = deque()
+    q.append((0, node))
+    mn, mx = None, None
+
+    while q:
+        depth, node = q.popleft()
+        # Current node is a leaf node
+        if not node.left and not node.right:
+            mx = depth if mx is None else max(mx, depth)
+            mn = depth if mn is None else min(mn, depth)
+            if mx - mn > 1:
+                return False
+        if node.left:
+            q.append((depth + 1, node.left))
+        if node.right:
+            q.append((depth + 1, node.right))
+
+    return mx - mn <= 1
+
+
+# Tests
+class Test(unittest.TestCase):
+    class BinaryTreeNode(object):
+        def __init__(self, value):
+            self.value = value
+            self.left = None
+            self.right = None
+
+        def insert_left(self, value):
+            self.left = Test.BinaryTreeNode(value)
+            return self.left
+
+        def insert_right(self, value):
+            self.right = Test.BinaryTreeNode(value)
+            return self.right
+
+    def test_full_tree(self):
+        tree = Test.BinaryTreeNode(5)
+        left = tree.insert_left(8)
+        right = tree.insert_right(6)
+        left.insert_left(1)
+        left.insert_right(2)
+        right.insert_left(3)
+        right.insert_right(4)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_both_leaves_at_the_same_depth(self):
+        tree = Test.BinaryTreeNode(3)
+        left = tree.insert_left(4)
+        right = tree.insert_right(2)
+        left.insert_left(1)
+        right.insert_right(9)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_leaf_heights_differ_by_one(self):
+        tree = Test.BinaryTreeNode(6)
+        left = tree.insert_left(1)
+        right = tree.insert_right(0)
+        right.insert_right(7)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_leaf_heights_differ_by_two(self):
+        tree = Test.BinaryTreeNode(6)
+        left = tree.insert_left(1)
+        right = tree.insert_right(0)
+        right_right = right.insert_right(7)
+        right_right.insert_right(8)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_three_leaves_total(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(5)
+        right = tree.insert_right(9)
+        right.insert_left(8)
+        right.insert_right(5)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_both_subtrees_superbalanced(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(5)
+        right = tree.insert_right(9)
+        right_left = right.insert_left(8)
+        right.insert_right(5)
+        right_left.insert_left(7)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_both_subtrees_superbalanced_two(self):
+        tree = Test.BinaryTreeNode(1)
+        left = tree.insert_left(2)
+        right = tree.insert_right(4)
+        left.insert_left(3)
+        left_right = left.insert_right(7)
+        left_right.insert_right(8)
+        right_right = right.insert_right(5)
+        right_right_right = right_right.insert_right(6)
+        right_right_right.insert_right(9)
+        result = is_balanced(tree)
+        self.assertFalse(result)
+
+    def test_only_one_node(self):
+        tree = Test.BinaryTreeNode(1)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+    def test_linked_list_tree(self):
+        tree = Test.BinaryTreeNode(1)
+        right = tree.insert_right(2)
+        right_right = right.insert_right(3)
+        right_right.insert_right(4)
+        result = is_balanced(tree)
+        self.assertTrue(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/bst-checker.py
+++ b/users/wpcarro/scratch/deepmind/part_two/bst-checker.py
@ -0,0 +1,110 @@
+import unittest
+from collections import deque
+
+
+# While this function solves the problem, it uses O(n) space since we're storing
+# all of the less-thans and greater-thans.
+def is_binary_search_tree_first_attempt(root):
+    q = deque()
+    q.append((set(), set(), root))
+
+    while q:
+        lts, gts, node = q.popleft()
+
+        if not all([node.value < lt for lt in lts]):
+            return False
+        if not all([node.value > gt for gt in gts]):
+            return False
+
+        if node.left:
+            q.append((lts | {node.value}, gts, node.left))
+        if node.right:
+            q.append((lts, gts | {node.value}, node.right))
+
+    return True
+
+
+# While I did not originally solve this problem this way, when I learned that I
+# could condense the space of my solution's runtime, I wrote this.
+def is_binary_search_tree(root):
+    q = deque()
+    q.append((None, None, root))
+
+    while q:
+        lt, gt, node = q.popleft()
+
+        if not lt is None and node.value >= lt:
+            return False
+        if not gt is None and node.value <= gt:
+            return False
+
+        if node.left:
+            q.append((node.value, gt, node.left))
+        if node.right:
+            q.append((lt, node.value, node.right))
+
+    return True
+
+
+# Tests
+class Test(unittest.TestCase):
+    class BinaryTreeNode(object):
+        def __init__(self, value):
+            self.value = value
+            self.left = None
+            self.right = None
+
+        def insert_left(self, value):
+            self.left = Test.BinaryTreeNode(value)
+            return self.left
+
+        def insert_right(self, value):
+            self.right = Test.BinaryTreeNode(value)
+            return self.right
+
+    def test_valid_full_tree(self):
+        tree = Test.BinaryTreeNode(50)
+        left = tree.insert_left(30)
+        right = tree.insert_right(70)
+        left.insert_left(10)
+        left.insert_right(40)
+        right.insert_left(60)
+        right.insert_right(80)
+        result = is_binary_search_tree(tree)
+        self.assertTrue(result)
+
+    def test_both_subtrees_valid(self):
+        tree = Test.BinaryTreeNode(50)
+        left = tree.insert_left(30)
+        right = tree.insert_right(80)
+        left.insert_left(20)
+        left.insert_right(60)
+        right.insert_left(70)
+        right.insert_right(90)
+        result = is_binary_search_tree(tree)
+        self.assertFalse(result)
+
+    def test_descending_linked_list(self):
+        tree = Test.BinaryTreeNode(50)
+        left = tree.insert_left(40)
+        left_left = left.insert_left(30)
+        left_left_left = left_left.insert_left(20)
+        left_left_left.insert_left(10)
+        result = is_binary_search_tree(tree)
+        self.assertTrue(result)
+
+    def test_out_of_order_linked_list(self):
+        tree = Test.BinaryTreeNode(50)
+        right = tree.insert_right(70)
+        right_right = right.insert_right(60)
+        right_right.insert_right(80)
+        result = is_binary_search_tree(tree)
+        self.assertFalse(result)
+
+    def test_one_node_tree(self):
+        tree = Test.BinaryTreeNode(50)
+        result = is_binary_search_tree(tree)
+        self.assertTrue(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/cafe-order-checker.py
+++ b/users/wpcarro/scratch/deepmind/part_two/cafe-order-checker.py
@ -0,0 +1,64 @@
+import unittest
+
+
+# Solution
+def is_first_come_first_served(xs, ys, zs):
+    i, j = 0, 0
+    for z in zs:
+        if i < len(xs) and z == xs[i]:
+            i += 1
+        elif j < len(ys) and z == ys[j]:
+            j += 1
+        else:
+            return False
+    return i == len(xs) and j == len(ys)
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_both_registers_have_same_number_of_orders(self):
+        result = is_first_come_first_served([1, 4, 5], [2, 3, 6],
+                                            [1, 2, 3, 4, 5, 6])
+        self.assertTrue(result)
+
+    def test_registers_have_different_lengths(self):
+        result = is_first_come_first_served([1, 5], [2, 3, 6], [1, 2, 6, 3, 5])
+        self.assertFalse(result)
+
+    def test_one_register_is_empty(self):
+        result = is_first_come_first_served([], [2, 3, 6], [2, 3, 6])
+        self.assertTrue(result)
+
+    def test_served_orders_is_missing_orders(self):
+        result = is_first_come_first_served([1, 5], [2, 3, 6], [1, 6, 3, 5])
+        self.assertFalse(result)
+
+    def test_served_orders_has_extra_orders(self):
+        result = is_first_come_first_served([1, 5], [2, 3, 6],
+                                            [1, 2, 3, 5, 6, 8])
+        self.assertFalse(result)
+
+    def test_one_register_has_extra_orders(self):
+        result = is_first_come_first_served([1, 9], [7, 8], [1, 7, 8])
+        self.assertFalse(result)
+
+    def test_one_register_has_unserved_orders(self):
+        result = is_first_come_first_served([55, 9], [7, 8], [1, 7, 8, 9])
+        self.assertFalse(result)
+
+    # Bonus
+    def test_handles_repeats(self):
+        actual = is_first_come_first_served([1, 2, 1], [3, 4, 5, 5],
+                                            [3, 4, 1, 5, 5, 2, 1])
+        self.assertTrue(actual)
+
+    def test_kitchen_didnt_serve(self):
+        actual = is_first_come_first_served([1, 2], [3, 4], [1, 3, 4])
+        self.assertFalse(actual)
+
+    def test_customer_didnt_pay(self):
+        actual = is_first_come_first_served([2], [3, 4], [1, 3, 4])
+        self.assertFalse(actual)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/coin.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/coin.ts
@ -0,0 +1,102 @@
+// The denomination of a coin.
+type Coin = number;
+
+// The amount of change remaining.
+type Amount = number;
+
+// Mapping of Coin -> Int
+type CoinBag = Map<Coin, number>;
+
+function createCoinBag(coins: Coin[]): CoinBag {
+  const result = new Map();
+
+  for (const coin of coins) {
+    result.set(coin, 0);
+  }
+
+  return result;
+}
+
+// This algorithm should work conceptual, but it does not actually
+// work. JavaScript uses reference equality when constructing a Set<Map<A,B>>,
+// so my result.size returns a higher number than I expect because it contains
+// many duplicate entries.
+//
+// Conceptually, I'm not sure this solution is optimal either -- even after I
+// can dedupe the entries in `result`.
+function changePossibilities(amt: Amount, coins: Coin[]): number {
+  if (amt === 0) {
+    return 1;
+  }
+  const result: Set<CoinBag> = new Set();
+
+  const q: [Coin, Amount, CoinBag][] = [];
+
+  for (const coin of coins) {
+    const bag = createCoinBag(coins);
+    bag.set(coin, 1);
+    q.push([coin, amt - coin, bag]);
+  }
+
+  while (q.length > 0) {
+    const [coin, amt, bag] = q.shift();
+
+    console.log([coin, amt, bag]);
+
+    if (amt === 0) {
+      result.add(bag);
+    } else if (amt < 0) {
+      continue;
+    } else {
+      for (const c of coins) {
+        const bagCopy = new Map(bag);
+        const value = bagCopy.get(c);
+        bagCopy.set(c, value + 1);
+        q.push([c, amt - c, bagCopy]);
+      }
+    }
+  }
+  console.log(result);
+  return result.size;
+}
+
+// Tests
+let desc = "sample input";
+let actual = changePossibilities(4, [1, 2, 3]);
+let expected = 4;
+assertEqual(actual, expected, desc);
+
+desc = "one way to make zero cents";
+actual = changePossibilities(0, [1, 2]);
+expected = 1;
+assertEqual(actual, expected, desc);
+
+desc = "no ways if no coins";
+actual = changePossibilities(1, []);
+expected = 0;
+assertEqual(actual, expected, desc);
+
+desc = "big coin value";
+actual = changePossibilities(5, [25, 50]);
+expected = 0;
+assertEqual(actual, expected, desc);
+
+desc = "big target amount";
+actual = changePossibilities(50, [5, 10]);
+expected = 6;
+assertEqual(actual, expected, desc);
+
+// I think InterviewCake designed this assertion to be computationally
+// expensive.
+desc = "change for one dollar";
+actual = changePossibilities(100, [1, 5, 10, 25, 50]);
+expected = 292;
+assertEqual(actual, expected, desc);
+
+function assertEqual(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/delete-node.py
+++ b/users/wpcarro/scratch/deepmind/part_two/delete-node.py
@ -0,0 +1,57 @@
+import unittest
+
+
+def delete_node(node):
+    if node.next:
+        node.value = node.next.value
+        node.next = node.next.next
+    else:
+        raise Exception(
+            "We cannot delete the last node in a linked list using this function"
+        )
+
+
+# Tests
+class Test(unittest.TestCase):
+    class LinkedListNode(object):
+        def __init__(self, value, next=None):
+            self.value = value
+            self.next = next
+
+        def get_values(self):
+            node = self
+            values = []
+            while node is not None:
+                values.append(node.value)
+                node = node.next
+            return values
+
+    def setUp(self):
+        self.fourth = Test.LinkedListNode(4)
+        self.third = Test.LinkedListNode(3, self.fourth)
+        self.second = Test.LinkedListNode(2, self.third)
+        self.first = Test.LinkedListNode(1, self.second)
+
+    def test_node_at_beginning(self):
+        delete_node(self.first)
+        actual = self.first.get_values()
+        expected = [2, 3, 4]
+        self.assertEqual(actual, expected)
+
+    def test_node_in_middle(self):
+        delete_node(self.second)
+        actual = self.first.get_values()
+        expected = [1, 3, 4]
+        self.assertEqual(actual, expected)
+
+    def test_node_at_end(self):
+        with self.assertRaises(Exception):
+            delete_node(self.fourth)
+
+    def test_one_node_in_list(self):
+        unique = Test.LinkedListNode(1)
+        with self.assertRaises(Exception):
+            delete_node(unique)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/find-duplicate-optimize-for-space-beast-mode.py
+++ b/users/wpcarro/scratch/deepmind/part_two/find-duplicate-optimize-for-space-beast-mode.py
@ -0,0 +1,114 @@
+import unittest
+
+
+################################################################################
+# InterviewCake's solution
+################################################################################
+def cycle_len(xs, i):
+    """
+    Returns the length of a cycle that contains no duplicate items.
+    """
+    result = 1
+    checkpt = i
+    current = xs[checkpt - 1]
+
+    while current != checkpt:
+        current = xs[current - 1]
+        result += 1
+
+    return result
+
+
+def theirs(xs):
+    """
+    This is InterviewCake's solution.
+    """
+    i = xs[-1]
+    for _ in range(len(xs) - 1):
+        i = xs[i - 1]
+
+    cycle_length = cycle_len(xs, i)
+
+    p0 = xs[-1]
+    p1 = xs[-1]
+    for _ in range(cycle_length):
+        p1 = xs[p1 - 1]
+
+    while p0 != p1:
+        p0 = xs[p0 - 1]
+        p1 = xs[p1 - 1]
+
+    print(p0, p1)
+
+    return p0
+
+
+################################################################################
+# My solution
+################################################################################
+def mine(xs):
+    """
+    This is the solution that I came up with, which differs from InterviewCake's
+    solution.
+    """
+    i = xs[-1]
+    offset = 1 if len(xs) % 2 == 0 else 2
+
+    for _ in range(len(xs) - offset):
+        i = xs[i - 1]
+
+    return i
+
+
+use_mine = True
+find_duplicate = mine if use_mine else theirs
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_just_the_repeated_number(self):
+        # len(xs) even
+        actual = find_duplicate([1, 1])
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_short_list(self):
+        # len(xs) even
+        actual = find_duplicate([1, 2, 3, 2])
+        expected = 2
+        self.assertEqual(actual, expected)
+
+    def test_medium_list(self):
+        # len(xs) even
+        actual = find_duplicate([1, 2, 5, 5, 5, 5])
+        expected = 5
+        self.assertEqual(actual, expected)
+
+    def test_long_list(self):
+        # len(xs) odd
+        actual = find_duplicate([4, 1, 4, 8, 3, 2, 7, 6, 5])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    ############################################################################
+    # Additional examples from InterviewCake.com
+    ############################################################################
+    def test_example_a(self):
+        # len(xs) even
+        actual = find_duplicate([3, 4, 2, 3, 1, 5])
+        expected = 3
+        self.assertTrue(actual, expected)
+
+    def test_example_b(self):
+        # len(xs) even
+        actual = find_duplicate([3, 1, 2, 2])
+        expected = 2
+        self.assertEqual(actual, expected)
+
+    def test_example_c(self):
+        # len(xs) odd BUT multiple duplicates
+        actual = find_duplicate([4, 3, 1, 1, 4])
+        self.assertTrue(actual in {1, 4})
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/find-duplicate-optimize-for-space.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/find-duplicate-optimize-for-space.ts
@ -0,0 +1,70 @@
+function findRepeatBruteForce(xs: Array<number>): number {
+  // InterviewCake asks us to write a function that optimizes for space. Using
+  // brute force, we can write a function that returns an answer using constant
+  // (i.e. O(1)) space at the cost of a quadratic (i.e. O(n^2)) runtime.
+  //
+  // I did not think of this myself; InterviewCake's "Tell me more" hints
+  // did. Since I think this idea is clever, I wrote a solution from memory to
+  // help me internalize the solution.
+  for (let i = 0; i < xs.length; i += 1) {
+    let seeking = xs[i];
+    for (let j = i + 1; j < xs.length; j += 1) {
+      if (xs[j] === seeking) {
+        return seeking;
+      }
+    }
+  }
+}
+
+function findRepeatSort(xs: Array<number>): number {
+  // This version first sorts xs, which gives the function a time-complexity of
+  // O(n*log(n)), which is better than the quadratic complexity of the
+  // brute-force solution. The space requirement here is constant.
+  //
+  // Since we need to sort xs in-place to avoid paying a O(n) space cost for
+  // storing the newly sorted xs, we're mutating our input. InterviewCake
+  // advises us to not mutate our input.
+  xs.sort();
+  let i = 0;
+  let j = 1;
+  for (; j < xs.length; ) {
+    if (xs[i] === xs[j]) {
+      return xs[i];
+    }
+    i += 1;
+    j += 1;
+  }
+}
+
+function findRepeat(xs: Array<number>): number {
+  return 0;
+}
+
+// Tests
+let desc = "just the repeated number";
+let actual = findRepeat([1, 1]);
+let expected = 1;
+assertEqual(actual, expected, desc);
+
+desc = "short array";
+actual = findRepeat([1, 2, 3, 2]);
+expected = 2;
+assertEqual(actual, expected, desc);
+
+desc = "medium array";
+actual = findRepeat([1, 2, 5, 5, 5, 5]);
+expected = 5;
+assertEqual(actual, expected, desc);
+
+desc = "long array";
+actual = findRepeat([4, 1, 4, 8, 3, 2, 7, 6, 5]);
+expected = 4;
+assertEqual(actual, expected, desc);
+
+function assertEqual(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/find-rotation-point.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/find-rotation-point.ts
@ -0,0 +1,68 @@
+function findRotationPoint(xs: Array<string>): number {
+  // Find the rotation point in the vector.
+  let beg = 0;
+  let end = xs.length - 1;
+
+  while (beg != end) {
+    let mid = beg + Math.floor((end - beg) / 2);
+
+    if (beg === mid) {
+      return xs[beg] < xs[end] ? beg : end;
+    }
+
+    if (xs[end] <= xs[mid]) {
+      beg = mid;
+      end = end;
+    } else {
+      beg = beg;
+      end = mid;
+    }
+  }
+
+  return beg;
+}
+
+// Tests
+let desc;
+let actual;
+let expected;
+
+desc = "small array one";
+actual = findRotationPoint(["cape", "cake"]);
+expected = 1;
+assertEquals(actual, expected, desc);
+
+desc = "small array two";
+actual = findRotationPoint(["cake", "cape"]);
+expected = 0;
+assertEquals(actual, expected, desc);
+
+desc = "medium array";
+actual = findRotationPoint(["grape", "orange", "plum", "radish", "apple"]);
+expected = 4;
+assertEquals(actual, expected, desc);
+
+desc = "large array";
+actual = findRotationPoint([
+  "ptolemaic",
+  "retrograde",
+  "supplant",
+  "undulate",
+  "xenoepist",
+  "asymptote",
+  "babka",
+  "banoffee",
+  "engender",
+  "karpatka",
+  "othellolagkage"
+]);
+expected = 5;
+assertEquals(actual, expected, desc);
+
+function assertEquals(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/graph-coloring.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/graph-coloring.ts
@ -0,0 +1,232 @@
+type Color = string;
+
+interface GraphNode {
+  label: string;
+  neighbors: Set<GraphNode>;
+  color: string;
+}
+
+class GraphNode {
+  constructor(label: string) {
+    this.label = label;
+    this.neighbors = new Set();
+    this.color = null;
+  }
+}
+
+interface Queue<A> {
+  xs: Array<A>;
+}
+
+class Queue<A> {
+  constructor() {
+    this.xs = [];
+  }
+  isEmpty(): boolean {
+    return this.xs.length === 0;
+  }
+  enqueue(x: A): void {
+    this.xs.push(x);
+  }
+  dequeue(): A {
+    return this.xs.shift();
+  }
+}
+
+type Graph = Array<GraphNode>;
+
+// Return a set of all of the colors from the neighbor nodes of `node`.
+function neighborColors(node: GraphNode): Set<Color> {
+  const result: Set<Color> = new Set();
+
+  for (const x of node.neighbors) {
+    if (typeof x.color === 'string') {
+      result.add(x.color);
+    }
+  }
+
+  return result;
+}
+
+// Returns the set difference between sets `xs`, and `ys`.
+function setDifference<A>(xs: Set<A>, ys: Set<A>): Set<A> {
+  const result: Set<A> = new Set();
+
+  for (const x of xs) {
+    if (!ys.has(x)) {
+      result.add(x);
+    }
+  }
+
+  return result;
+}
+
+// Returns an element from the set, `xs`.
+// Throwns an error if `xs` is an empty set.
+function choose<A>(xs: Set<A>): A {
+  if (xs.size === 0) {
+    throw new Error('Cannot choose an element from an empty set.');
+  } else {
+    return xs.values().next().value;
+  }
+}
+
+// Returns true if `node` is present in `node.neighbors`.
+function isCyclic(node: GraphNode): boolean {
+  for (const x of node.neighbors) {
+    if (x === node) {
+      return true;
+    }
+  }
+}
+
+function colorGraph(graph: Graph, colors: Array<Color>): void {
+  const allColors = new Set(colors);
+
+  for (const node of graph) {
+    if (isCyclic(node)) {
+      throw new Error('InterviewCake would like me to invalidate this');
+    }
+    if (typeof node.color !== 'string') {
+      node.color = choose(setDifference(allColors, neighborColors(node)));
+    }
+  }
+}
+
+
+// Tests
+const colors = ['red', 'green', 'blue', 'orange', 'yellow', 'white'];
+
+let graph = [];
+{
+  const nodeA = new GraphNode('A');
+  const nodeB = new GraphNode('B');
+  const nodeC = new GraphNode('C');
+  const nodeD = new GraphNode('D');
+  nodeA.neighbors.add(nodeB);
+  nodeB.neighbors.add(nodeA);
+  nodeB.neighbors.add(nodeC);
+  nodeC.neighbors.add(nodeB);
+  nodeC.neighbors.add(nodeD);
+  nodeD.neighbors.add(nodeC);
+  graph = [nodeA, nodeB, nodeC, nodeD];
+}
+colorGraph(graph, colors);
+assertEqual(validateGraphColoring(graph), true, 'line graph');
+
+{
+  const nodeA = new GraphNode('A');
+  const nodeB = new GraphNode('B');
+  const nodeC = new GraphNode('C');
+  const nodeD = new GraphNode('D');
+  nodeA.neighbors.add(nodeB);
+  nodeB.neighbors.add(nodeA);
+  nodeC.neighbors.add(nodeD);
+  nodeD.neighbors.add(nodeC);
+  graph = [nodeA, nodeB, nodeC, nodeD];
+}
+colorGraph(graph, colors);
+assertEqual(validateGraphColoring(graph), true, 'separate graph');
+
+{
+  const nodeA = new GraphNode('A');
+  const nodeB = new GraphNode('B');
+  const nodeC = new GraphNode('C');
+  nodeA.neighbors.add(nodeB);
+  nodeA.neighbors.add(nodeC);
+  nodeB.neighbors.add(nodeA);
+  nodeB.neighbors.add(nodeC);
+  nodeC.neighbors.add(nodeA);
+  nodeC.neighbors.add(nodeB);
+  graph = [nodeA, nodeB, nodeC];
+}
+colorGraph(graph, colors);
+assertEqual(validateGraphColoring(graph), true, 'triangle graph');
+
+{
+  const nodeA = new GraphNode('A');
+  const nodeB = new GraphNode('B');
+  const nodeC = new GraphNode('C');
+  const nodeD = new GraphNode('D');
+  const nodeE = new GraphNode('E');
+  nodeA.neighbors.add(nodeB);
+  nodeA.neighbors.add(nodeC);
+  nodeB.neighbors.add(nodeA);
+  nodeB.neighbors.add(nodeC);
+  nodeB.neighbors.add(nodeD);
+  nodeB.neighbors.add(nodeE);
+  nodeC.neighbors.add(nodeA);
+  nodeC.neighbors.add(nodeB);
+  nodeC.neighbors.add(nodeD);
+  nodeC.neighbors.add(nodeE);
+  nodeD.neighbors.add(nodeB);
+  nodeD.neighbors.add(nodeC);
+  nodeD.neighbors.add(nodeE);
+  nodeE.neighbors.add(nodeB);
+  nodeE.neighbors.add(nodeC);
+  nodeE.neighbors.add(nodeD);
+  graph = [nodeA, nodeB, nodeC, nodeD, nodeE];
+}
+colorGraph(graph, colors);
+assertEqual(validateGraphColoring(graph), true, 'envelope graph');
+
+{
+  const nodeA = new GraphNode('A');
+  nodeA.neighbors.add(nodeA);
+  graph = [nodeA];
+}
+assertThrows(() => {
+  colorGraph(graph, colors);
+}, 'loop graph');
+
+function validateGraphColoring(graph) {
+
+  const maxDegree = Math.max(...graph.map(node => node.neighbors.size));
+
+  const colorsUsed = new Set();
+
+  graph.forEach(node => {
+    colorsUsed.add(node.color);
+  });
+
+  if (colorsUsed.has(null)) {
+    return false;
+  }
+
+  if (colorsUsed.size > maxDegree + 1) {
+    return false;
+  }
+
+  let badEdges = 0;
+
+  graph.forEach(node => {
+    node.neighbors.forEach(neighbor => {
+      if (neighbor.color === node.color) {
+        badEdges += 1;
+      }
+    });
+  });
+
+  if (badEdges > 0) {
+    return false;
+  }
+
+  return true;
+}
+
+function assertEqual(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
+
+function assertThrows(func, desc) {
+  try {
+    func();
+    console.log(`${desc} ... FAIL`);
+  } catch (e) {
+    console.log(`${desc} ... PASS`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/highest-product-of-3.py
+++ b/users/wpcarro/scratch/deepmind/part_two/highest-product-of-3.py
@ -0,0 +1,81 @@
+import unittest
+import sys
+import trace
+
+
+def highest_product_of_3(xs):
+    if len(xs) < 3:
+        raise Exception("List needs to contain at least three elements.")
+    hp3 = xs[0] * xs[1] * xs[2]
+    hp2 = xs[0] * xs[1]
+    lp2 = xs[0] * xs[1]
+    hn = max(xs[0], xs[1])
+    ln = min(xs[0], xs[1])
+    for x in xs[2:]:
+        hp3 = max(hp3, hp2 * x, lp2 * x)
+        hp2 = max(hp2, hn * x, ln * x)
+        lp2 = min(lp2, hn * x, ln * x)
+        hn = max(hn, x)
+        ln = min(ln, x)
+    return hp3
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_short_list(self):
+        actual = highest_product_of_3([1, 2, 3, 4])
+        expected = 24
+        self.assertEqual(actual, expected)
+
+    def test_longer_list(self):
+        actual = highest_product_of_3([6, 1, 3, 5, 7, 8, 2])
+        expected = 336
+        self.assertEqual(actual, expected)
+
+    def test_list_has_one_negative(self):
+        actual = highest_product_of_3([-5, 4, 8, 2, 3])
+        expected = 96
+        self.assertEqual(actual, expected)
+
+    def test_list_has_two_negatives(self):
+        actual = highest_product_of_3([-10, 1, 3, 2, -10])
+        expected = 300
+        self.assertEqual(actual, expected)
+
+    def test_list_is_all_negatives(self):
+        actual = highest_product_of_3([-5, -1, -3, -2])
+        expected = -6
+        self.assertEqual(actual, expected)
+
+    def test_error_with_empty_list(self):
+        with self.assertRaises(Exception):
+            highest_product_of_3([])
+
+    def test_error_with_one_number(self):
+        with self.assertRaises(Exception):
+            highest_product_of_3([1])
+
+    def test_error_with_two_numbers(self):
+        with self.assertRaises(Exception):
+            highest_product_of_3([1, 1])
+
+    def test_custom(self):
+        actual = highest_product_of_3([9, 5, 2, 1, 7, 3])
+        expected = 9 * 7 * 5
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
+
+
+def main():
+    highest_product_of_3([-5, -1, -3, -2])
+
+
+tracer = trace.Trace(ignoredirs=[sys.prefix, sys.exec_prefix],
+                     trace=0,
+                     count=1)
+
+tracer.run('main()')
+r = tracer.results()
+r.write_results(show_missing=True, coverdir=".")
--- a/users/wpcarro/scratch/deepmind/part_two/inflight-entertainment.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/inflight-entertainment.ts
@ -0,0 +1,85 @@
+function canTwoMoviesFillFlightBonus(
+  xs: Array<number>,
+  duration: number
+): boolean {
+  // Returns true if two movies exist that can fill the flight duration +/- 20
+  // minutes.
+  const seeking = {};
+
+  for (let x of xs) {
+    for (let i = 0; i < 40; i += 1) {
+      if (seeking[x + i + 1]) {
+        return true;
+      }
+    }
+    for (let i = 1; i <= 20; i += 1) {
+      seeking[duration - x - i] = true;
+      seeking[duration - x + i] = true;
+    }
+  }
+
+  return false;
+}
+
+function canTwoMoviesFillFlight(xs: Array<number>, duration: number): boolean {
+  const seeking = {};
+
+  for (let x of xs) {
+    if (seeking[x]) {
+      return true;
+    } else {
+      seeking[duration - x] = true;
+    }
+  }
+
+  return false;
+}
+
+// Tests
+let desc = "short flight";
+let actual = canTwoMoviesFillFlight([2, 4], 1);
+let expected = false;
+assertEquals(actual, expected, desc);
+
+desc = "long flight";
+actual = canTwoMoviesFillFlight([2, 4], 6);
+expected = true;
+assertEquals(actual, expected, desc);
+
+desc = "one movie half flight length";
+actual = canTwoMoviesFillFlight([3, 8], 6);
+expected = false;
+assertEquals(actual, expected, desc);
+
+desc = "two movies half flight length";
+actual = canTwoMoviesFillFlight([3, 8, 3], 6);
+expected = true;
+assertEquals(actual, expected, desc);
+
+desc = "lots of possible pairs";
+actual = canTwoMoviesFillFlight([1, 2, 3, 4, 5, 6], 7);
+expected = true;
+assertEquals(actual, expected, desc);
+
+desc = "not using first movie";
+actual = canTwoMoviesFillFlight([4, 3, 2], 5);
+expected = true;
+assertEquals(actual, expected, desc);
+
+desc = "only one movie";
+actual = canTwoMoviesFillFlight([6], 6);
+expected = false;
+assertEquals(actual, expected, desc);
+
+desc = "no movies";
+actual = canTwoMoviesFillFlight([], 2);
+expected = false;
+assertEquals(actual, expected, desc);
+
+function assertEquals(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/merge-sorted-arrays.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/merge-sorted-arrays.ts
@ -0,0 +1,63 @@
+function mergeArrays(xs: Array<number>, ys: Array<number>): Array<number> {
+  let i = 0;
+  let j = 0;
+  const result = [];
+
+  for (let q = 0; q < xs.length + ys.length; q += 1) {
+    if (i === xs.length) {
+      while (j < ys.length) {
+        result.push(ys[j]);
+        j += 1;
+      }
+    } else if (j === ys.length) {
+      while (i < xs.length) {
+        result.push(xs[i]);
+        i += 1;
+      }
+    } else if (xs[i] < ys[j]) {
+      result.push(xs[i]);
+      i += 1;
+    } else {
+      result.push(ys[j]);
+      j += 1;
+    }
+  }
+
+  return result;
+}
+
+// Tests
+let desc = "both arrays are empty";
+let actual = mergeArrays([], []);
+let expected = [];
+assertDeepEqual(actual, expected, desc);
+
+desc = "first array is empty";
+actual = mergeArrays([], [1, 2, 3]);
+expected = [1, 2, 3];
+assertDeepEqual(actual, expected, desc);
+
+desc = "second array is empty";
+actual = mergeArrays([5, 6, 7], []);
+expected = [5, 6, 7];
+assertDeepEqual(actual, expected, desc);
+
+desc = "both arrays have some numbers";
+actual = mergeArrays([2, 4, 6], [1, 3, 7]);
+expected = [1, 2, 3, 4, 6, 7];
+assertDeepEqual(actual, expected, desc);
+
+desc = "arrays are different lengths";
+actual = mergeArrays([2, 4, 6, 8], [1, 7]);
+expected = [1, 2, 4, 6, 7, 8];
+assertDeepEqual(actual, expected, desc);
+
+function assertDeepEqual(a: Array<number>, b: Array<number>, desc: string) {
+  const aStr = JSON.stringify(a);
+  const bStr = JSON.stringify(b);
+  if (aStr !== bStr) {
+    console.log(`${desc} ... FAIL: ${aStr} != ${bStr}`);
+  } else {
+    console.log(`${desc} ... PASS`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/merging-ranges.py
+++ b/users/wpcarro/scratch/deepmind/part_two/merging-ranges.py
@ -0,0 +1,115 @@
+import unittest
+import timeit
+
+
+# Solution that uses O(n) space to store the result.
+def not_in_place(xs):
+    xs.sort()
+    result = [xs[0]]
+    for ca, cb in xs[1:]:
+        pa, pb = result[-1]
+        if ca <= pb:
+            result[-1] = (pa, max(pb, cb))
+        else:
+            result.append((ca, cb))
+    return result
+
+
+# Solution that uses O(1) space to store the result.
+def in_place(xs):
+    xs.sort()
+    i = 0
+    j = i + 1
+    while j < len(xs):
+        pa, pb = xs[i]
+        ca, cb = xs[j]
+        if ca <= pb:
+            xs[i] = (pa, max(pb, cb))
+            del xs[j]
+        else:
+            i = j
+            j += 1
+    return xs
+
+
+def test_nip():
+    inputs = [
+        [(1, 3), (2, 4)],
+        [(5, 6), (6, 8)],
+        [(1, 8), (2, 5)],
+        [(1, 3), (4, 8)],
+        [(1, 4), (2, 5), (5, 8)],
+        [(5, 8), (1, 4), (6, 8)],
+        [(1, 10), (2, 5), (6, 8), (9, 10), (10, 12)],
+        [(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)],
+    ]
+    for x in inputs:
+        not_in_place(x)
+
+
+def test_ip():
+    inputs = [
+        [(1, 3), (2, 4)],
+        [(5, 6), (6, 8)],
+        [(1, 8), (2, 5)],
+        [(1, 3), (4, 8)],
+        [(1, 4), (2, 5), (5, 8)],
+        [(5, 8), (1, 4), (6, 8)],
+        [(1, 10), (2, 5), (6, 8), (9, 10), (10, 12)],
+        [(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)],
+    ]
+    for x in inputs:
+        in_place(x)
+
+
+merge_ranges = in_place
+
+setup = 'from __main__ import test_nip, test_ip'
+print(timeit.timeit('test_nip()', number=10000, setup=setup))
+print(timeit.timeit('test_ip()', number=10000, setup=setup))
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_meetings_overlap(self):
+        actual = merge_ranges([(1, 3), (2, 4)])
+        expected = [(1, 4)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_touch(self):
+        actual = merge_ranges([(5, 6), (6, 8)])
+        expected = [(5, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meeting_contains_other_meeting(self):
+        actual = merge_ranges([(1, 8), (2, 5)])
+        expected = [(1, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_stay_separate(self):
+        actual = merge_ranges([(1, 3), (4, 8)])
+        expected = [(1, 3), (4, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_multiple_merged_meetings(self):
+        actual = merge_ranges([(1, 4), (2, 5), (5, 8)])
+        expected = [(1, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_meetings_not_sorted(self):
+        actual = merge_ranges([(5, 8), (1, 4), (6, 8)])
+        expected = [(1, 4), (5, 8)]
+        self.assertEqual(actual, expected)
+
+    def test_one_long_meeting_contains_smaller_meetings(self):
+        actual = merge_ranges([(1, 10), (2, 5), (6, 8), (9, 10), (10, 12)])
+        expected = [(1, 12)]
+        self.assertEqual(actual, expected)
+
+    def test_sample_input(self):
+        actual = merge_ranges([(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)])
+        expected = [(0, 1), (3, 8), (9, 12)]
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/mesh-message.py
+++ b/users/wpcarro/scratch/deepmind/part_two/mesh-message.py
@ -0,0 +1,183 @@
+import unittest
+from collections import deque
+from heapq import heappush, heappop
+
+
+################################################################################
+# InterviewCake.com
+################################################################################
+# construct_path :: Map String String -> String -> String -> [String]
+def construct_path(paths, beg, end):
+    """
+    Reconstruct the path from `beg` to `end`.
+    """
+    result = []
+    current = end
+
+    print(paths)
+    print(beg, end)
+    print('-----')
+    while current:
+        result.append(current)
+        current = paths[current]
+
+    result.reverse()
+    return result
+
+
+def get_path_ic(graph, beg, end):
+    """
+    InterviewCake uses a dictionary and back-tracking to store and reconstruct
+    the path instead of storing the path as state on each node.
+    This reduces the memory costs. See get_path_bft for an example of this less
+    optimal solution.
+    """
+    if beg not in graph:
+        raise Exception('Origin node absent from graph.')
+
+    if end not in graph:
+        raise Exception('Destination node absent from graph.')
+
+    q = deque()
+    q.append(beg)
+    paths = {beg: None}
+
+    while q:
+        node = q.popleft()
+
+        if node == end:
+            print(graph)
+            return construct_path(paths, beg, end)
+
+        for x in graph[node]:
+            if x not in paths:
+                paths[x] = node
+                q.append(x)
+
+    return None
+
+
+################################################################################
+# Per-node state
+################################################################################
+def get_path_bft(graph, beg, end):
+    """
+    Here we find the shortest path from `beg` to `end` in `graph` by doing a BFT
+    from beg to end and storing the path state alongside each node in the queue.
+    """
+    if beg not in graph:
+        raise Exception('Origin node absent from graph.')
+
+    if end not in graph:
+        raise Exception('Destination node absent from graph.')
+
+    q = deque()
+    seen = set()
+    q.append([beg])
+
+    while q:
+        path = q.popleft()
+        node = path[-1]
+        seen.add(node)
+
+        if node == end:
+            return path
+
+        for x in graph[node]:
+            if x not in seen:
+                q.append(path + [x])
+
+
+################################################################################
+# Dijkstra's Algorithm
+################################################################################
+def get_path(graph, beg, end):
+    """
+    Here we find the shortest path using Dijkstra's algorithm, which is my
+    favorite solution.
+    """
+    if beg not in graph:
+        raise Exception(
+            'The origin node, {}, is not present in the graph'.format(beg))
+
+    if end not in graph:
+        raise Exception(
+            'The origin node, {}, is not present in the graph'.format(end))
+
+    q = []
+    seen = set()
+    heappush(q, (1, [beg]))
+
+    while q:
+        weight, path = heappop(q)
+        node = path[-1]
+        seen.add(node)
+
+        if node == end:
+            return path
+
+        for x in graph[node]:
+            if x not in seen:
+                heappush(q, (weight + 1, path + [x]))
+
+    return None
+
+
+# Tests
+class Test(unittest.TestCase):
+    def setUp(self):
+        self.graph = {
+            'a': ['b', 'c', 'd'],
+            'b': ['a', 'd'],
+            'c': ['a', 'e'],
+            'd': ['b', 'a'],
+            'e': ['c'],
+            'f': ['g'],
+            'g': ['f'],
+        }
+
+    def test_two_hop_path_1(self):
+        actual = get_path(self.graph, 'a', 'e')
+        expected = ['a', 'c', 'e']
+        self.assertEqual(actual, expected)
+
+    def test_two_hop_path_2(self):
+        actual = get_path(self.graph, 'd', 'c')
+        expected = ['d', 'a', 'c']
+        self.assertEqual(actual, expected)
+
+    def test_one_hop_path_1(self):
+        actual = get_path(self.graph, 'a', 'c')
+        expected = ['a', 'c']
+        self.assertEqual(actual, expected)
+
+    def test_one_hop_path_2(self):
+        actual = get_path(self.graph, 'f', 'g')
+        expected = ['f', 'g']
+        self.assertEqual(actual, expected)
+
+    def test_one_hop_path_3(self):
+        actual = get_path(self.graph, 'g', 'f')
+        expected = ['g', 'f']
+        self.assertEqual(actual, expected)
+
+    def test_zero_hop_path(self):
+        actual = get_path(self.graph, 'a', 'a')
+        expected = ['a']
+        self.assertEqual(actual, expected)
+
+    def test_no_path(self):
+        actual = get_path(self.graph, 'a', 'f')
+        expected = None
+        self.assertEqual(actual, expected)
+
+    def test_start_node_not_present(self):
+        with self.assertRaises(Exception):
+            get_path(self.graph, 'h', 'a')
+
+    def test_end_node_not_present(self):
+        with self.assertRaises(Exception):
+            get_path(self.graph, 'a', 'h')
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/misc/matrix-traversals.py
+++ b/users/wpcarro/scratch/deepmind/part_two/misc/matrix-traversals.py
@ -0,0 +1,104 @@
+# Herein I'm practicing two-dimensional matrix traversals in all directions of
+# which I can conceive:
+# 0. T -> B; L -> R
+# 1. T -> B; R -> L
+# 2. B -> T; L -> R
+# 3. B -> T; R -> L
+#
+# Commentary:
+# When I think of matrices, I'm reminded of cartesian planes. I think of the
+# cells as (X,Y) coordinates. This has been a pitfall for me because matrices
+# are usually encoded in the opposite way. That is, to access a cell at the
+# coordinates (X,Y) given a matrix M, you index M like this: M[Y][X]. To attempt
+# to avoid this confusion, instead of saying X and Y, I will prefer saying
+# "column" and "row".
+#
+# When traversing a matrix, you typically traverse vertically and then
+# horizontally; in other words, the rows come first followed by the columns. As
+# such, I'd like to refer to traversal orders as "top-to-bottom, left-to-right"
+# rather than "left-to-right, top-to-bottom".
+#
+# These practices are all in an attempt to rewire my thinking.
+
+# This is a list of matrices where the index of a matrix corresponds to the
+# order in which it should be traversed to produce the sequence:
+# [1,2,3,4,5,6,7,8,9].
+boards = [[[1, 2, 3], [4, 5, 6], [7, 8, 9]], [[3, 2, 1], [6, 5, 4], [9, 8, 7]],
+          [[7, 8, 9], [4, 5, 6], [1, 2, 3]], [[9, 8, 7], [6, 5, 4], [3, 2, 1]]]
+
+# T -> B; L -> R
+board = boards[0]
+result = []
+for row in board:
+    for col in row:
+        result.append(col)
+print(result)
+
+# T -> B; R -> L
+board = boards[1]
+result = []
+for row in board:
+    for col in reversed(row):
+        result.append(col)
+print(result)
+
+# B -> T; L -> R
+board = boards[2]
+result = []
+for row in reversed(board):
+    for col in row:
+        result.append(col)
+print(result)
+
+# B -> T; R -> L
+board = boards[3]
+result = []
+for row in reversed(board):
+    for col in reversed(row):
+        result.append(col)
+print(result)
+
+################################################################################
+# Neighbors
+################################################################################
+
+import random
+
+
+# Generate a matrix of size `rows` x `cols` where each cell contains an item
+# randomly selected from `xs`.
+def generate_board(rows, cols, xs):
+    result = []
+    for _ in range(rows):
+        row = []
+        for _ in range(cols):
+            row.append(random.choice(xs))
+        result.append(row)
+    return result
+
+
+# Print the `board` to the screen.
+def print_board(board):
+    print('\n'.join([' '.join(row) for row in board]))
+
+
+board = generate_board(4, 5, ['R', 'G', 'B'])
+print_board(board)
+
+
+# Return all of the cells horizontally and vertically accessible from a starting
+# cell at `row`, `col` in `board`.
+def neighbors(row, col, board):
+    result = {'top': [], 'bottom': [], 'left': [], 'right': []}
+    for i in range(row - 1, -1, -1):
+        result['top'].append(board[i][col])
+    for i in range(row + 1, len(board)):
+        result['bottom'].append(board[i][col])
+    for i in range(col - 1, -1, -1):
+        result['left'].append(board[row][i])
+    for i in range(col + 1, len(board[0])):
+        result['right'].append(board[row][i])
+    return result
+
+
+print(neighbors(1, 2, board))
--- a/users/wpcarro/scratch/deepmind/part_two/nth-fibonacci.py
+++ b/users/wpcarro/scratch/deepmind/part_two/nth-fibonacci.py
@ -0,0 +1,72 @@
+import unittest
+
+
+# Compute the fibonacci using a bottom-up algorithm.
+def fib(n):
+    if n < 0:
+        raise Error('Cannot call fibonacci with negative values')
+    cache = [0, 1]
+    for i in range(n):
+        cache[0], cache[1] = cache[1], cache[0] + cache[1]
+    return cache[0]
+
+
+# Compute the fibonacci using memoization.
+def fib_memoized(n):
+    cache = {
+        0: 0,
+        1: 1,
+    }
+
+    def do_fib(n):
+        if n < 0:
+            raise Error('The fib function does not support negative inputs')
+
+        if n in cache:
+            return cache[n]
+
+        cache[n - 1] = do_fib(n - 1)
+        cache[n - 2] = do_fib(n - 2)
+        return cache[n - 1] + cache[n - 2]
+
+    return do_fib(n)
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_zeroth_fibonacci(self):
+        actual = fib(0)
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_first_fibonacci(self):
+        actual = fib(1)
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_second_fibonacci(self):
+        actual = fib(2)
+        expected = 1
+        self.assertEqual(actual, expected)
+
+    def test_third_fibonacci(self):
+        actual = fib(3)
+        expected = 2
+        self.assertEqual(actual, expected)
+
+    def test_fifth_fibonacci(self):
+        actual = fib(5)
+        expected = 5
+        self.assertEqual(actual, expected)
+
+    def test_tenth_fibonacci(self):
+        actual = fib(10)
+        expected = 55
+        self.assertEqual(actual, expected)
+
+    def test_negative_fibonacci(self):
+        with self.assertRaises(Exception):
+            fib(-1)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/package-lock.json
+++ b/users/wpcarro/scratch/deepmind/part_two/package-lock.json
@ -0,0 +1,79 @@
+{
+  "name": "deepmind-part-two",
+  "version": "1.0.0",
+  "lockfileVersion": 1,
+  "requires": true,
+  "dependencies": {
+    "arg": {
+      "version": "4.1.3",
+      "resolved": "https://registry.npmjs.org/arg/-/arg-4.1.3.tgz",
+      "integrity": "sha512-58S9QDqG0Xx27YwPSt9fJxivjYl432YCwfDMfZ+71RAqUrZef7LrKQZ3LHLOwCS4FLNBplP533Zx895SeOCHvA==",
+      "dev": true
+    },
+    "buffer-from": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/buffer-from/-/buffer-from-1.1.1.tgz",
+      "integrity": "sha512-MQcXEUbCKtEo7bhqEs6560Hyd4XaovZlO/k9V3hjVUF/zwW7KBVdSK4gIt/bzwS9MbR5qob+F5jusZsb0YQK2A==",
+      "dev": true
+    },
+    "diff": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/diff/-/diff-4.0.2.tgz",
+      "integrity": "sha512-58lmxKSA4BNyLz+HHMUzlOEpg09FV+ev6ZMe3vJihgdxzgcwZ8VoEEPmALCZG9LmqfVoNMMKpttIYTVG6uDY7A==",
+      "dev": true
+    },
+    "make-error": {
+      "version": "1.3.5",
+      "resolved": "https://registry.npmjs.org/make-error/-/make-error-1.3.5.tgz",
+      "integrity": "sha512-c3sIjNUow0+8swNwVpqoH4YCShKNFkMaw6oH1mNS2haDZQqkeZFlHS3dhoeEbKKmJB4vXpJucU6oH75aDYeE9g==",
+      "dev": true
+    },
+    "prettier": {
+      "version": "2.0.2",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-2.0.2.tgz",
+      "integrity": "sha512-5xJQIPT8BraI7ZnaDwSbu5zLrB6vvi8hVV58yHQ+QK64qrY40dULy0HSRlQ2/2IdzeBpjhDkqdcFBnFeDEMVdg==",
+      "dev": true
+    },
+    "source-map": {
+      "version": "0.6.1",
+      "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+      "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+      "dev": true
+    },
+    "source-map-support": {
+      "version": "0.5.16",
+      "resolved": "https://registry.npmjs.org/source-map-support/-/source-map-support-0.5.16.tgz",
+      "integrity": "sha512-efyLRJDr68D9hBBNIPWFjhpFzURh+KJykQwvMyW5UiZzYwoF6l4YMMDIJJEyFWxWCqfyxLzz6tSfUFR+kXXsVQ==",
+      "dev": true,
+      "requires": {
+        "buffer-from": "^1.0.0",
+        "source-map": "^0.6.0"
+      }
+    },
+    "ts-node": {
+      "version": "8.6.2",
+      "resolved": "https://registry.npmjs.org/ts-node/-/ts-node-8.6.2.tgz",
+      "integrity": "sha512-4mZEbofxGqLL2RImpe3zMJukvEvcO1XP8bj8ozBPySdCUXEcU5cIRwR0aM3R+VoZq7iXc8N86NC0FspGRqP4gg==",
+      "dev": true,
+      "requires": {
+        "arg": "^4.1.0",
+        "diff": "^4.0.1",
+        "make-error": "^1.1.1",
+        "source-map-support": "^0.5.6",
+        "yn": "3.1.1"
+      }
+    },
+    "typescript": {
+      "version": "3.7.5",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.7.5.tgz",
+      "integrity": "sha512-/P5lkRXkWHNAbcJIiHPfRoKqyd7bsyCma1hZNUGfn20qm64T6ZBlrzprymeu918H+mB/0rIg2gGK/BXkhhYgBw==",
+      "dev": true
+    },
+    "yn": {
+      "version": "3.1.1",
+      "resolved": "https://registry.npmjs.org/yn/-/yn-3.1.1.tgz",
+      "integrity": "sha512-Ux4ygGWsu2c7isFWe8Yu1YluJmqVhxqK2cLXNQA5AcC3QfbGNpM7fu0Y8b/z16pXLnFxZYvWhd3fhBY9DLmC6Q==",
+      "dev": true
+    }
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/package.json
+++ b/users/wpcarro/scratch/deepmind/part_two/package.json
@ -0,0 +1,16 @@
+{
+  "name": "deepmind-part-two",
+  "version": "1.0.0",
+  "description": "Practicing coding interview questions",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "William Carroll",
+  "license": "MIT",
+  "devDependencies": {
+    "prettier": "^2.0.2",
+    "ts-node": "^8.6.2",
+    "typescript": "^3.7.5"
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/permutation-palindrome.py
+++ b/users/wpcarro/scratch/deepmind/part_two/permutation-palindrome.py
@ -0,0 +1,37 @@
+import unittest
+from collections import Counter
+
+
+def has_palindrome_permutation(xs):
+    vs = Counter(xs).values()
+    return len([v for v in vs if v % 2 == 1]) in {0, 1}
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_permutation_with_odd_number_of_chars(self):
+        result = has_palindrome_permutation('aabcbcd')
+        self.assertTrue(result)
+
+    def test_permutation_with_even_number_of_chars(self):
+        result = has_palindrome_permutation('aabccbdd')
+        self.assertTrue(result)
+
+    def test_no_permutation_with_odd_number_of_chars(self):
+        result = has_palindrome_permutation('aabcd')
+        self.assertFalse(result)
+
+    def test_no_permutation_with_even_number_of_chars(self):
+        result = has_palindrome_permutation('aabbcd')
+        self.assertFalse(result)
+
+    def test_empty_string(self):
+        result = has_palindrome_permutation('')
+        self.assertTrue(result)
+
+    def test_one_character_string(self):
+        result = has_palindrome_permutation('a')
+        self.assertTrue(result)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/product-of-other-numbers.py
+++ b/users/wpcarro/scratch/deepmind/part_two/product-of-other-numbers.py
@ -0,0 +1,68 @@
+import unittest
+
+
+# get_products_of_all_ints_except_at_index :: [Int] -> [Int]
+def get_products_of_all_ints_except_at_index(xs):
+    n = len(xs)
+    if n < 2:
+        raise Exception("Cannot computer without 2 or elements")
+    # lhs
+    befores = [None] * n
+    befores[0] = 1
+    for i in range(1, n):
+        befores[i] = befores[i - 1] * xs[i - 1]
+
+    # rhs
+    afters = [None] * n
+    afters[-1] = 1
+    for i in range(n - 2, -1, -1):
+        afters[i] = afters[i + 1] * xs[i + 1]
+
+    result = [None] * n
+    for i in range(n):
+        result[i] = befores[i] * afters[i]
+    return result
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_small_list(self):
+        actual = get_products_of_all_ints_except_at_index([1, 2, 3])
+        expected = [6, 3, 2]
+        self.assertEqual(actual, expected)
+
+    def test_longer_list(self):
+        actual = get_products_of_all_ints_except_at_index([8, 2, 4, 3, 1, 5])
+        expected = [120, 480, 240, 320, 960, 192]
+        self.assertEqual(actual, expected)
+
+    def test_list_has_one_zero(self):
+        actual = get_products_of_all_ints_except_at_index([6, 2, 0, 3])
+        expected = [0, 0, 36, 0]
+        self.assertEqual(actual, expected)
+
+    def test_list_has_two_zeros(self):
+        actual = get_products_of_all_ints_except_at_index([4, 0, 9, 1, 0])
+        expected = [0, 0, 0, 0, 0]
+        self.assertEqual(actual, expected)
+
+    def test_one_negative_number(self):
+        actual = get_products_of_all_ints_except_at_index([-3, 8, 4])
+        expected = [32, -12, -24]
+        self.assertEqual(actual, expected)
+
+    def test_all_negative_numbers(self):
+        actual = get_products_of_all_ints_except_at_index([-7, -1, -4, -2])
+        expected = [-8, -56, -14, -28]
+        self.assertEqual(actual, expected)
+
+    def test_error_with_empty_list(self):
+        with self.assertRaises(Exception):
+            get_products_of_all_ints_except_at_index([])
+
+    def test_error_with_one_number(self):
+        with self.assertRaises(Exception):
+            get_products_of_all_ints_except_at_index([1])
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/recursive-string-permutations.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/recursive-string-permutations.ts
@ -0,0 +1,85 @@
+// Returns a new string comprised of every characters in `xs` except for the
+// character at `i`.
+function everyOtherChar(xs: string, i: number): string[] {
+  const result = [];
+
+  for (let j = 0; j < xs.length; j += 1) {
+    if (i !== j) {
+      result.push(xs[j]);
+    }
+  }
+
+  return [xs[i], result.join('')];
+}
+
+function getPermutations(xs: string): Set<string> {
+  if (xs === '') {
+    return new Set(['']);
+  }
+
+  const result: Set<string> = new Set;
+
+  for (let i = 0; i < xs.length; i += 1) {
+    const [char, rest] = everyOtherChar(xs, i);
+    const perms = getPermutations(rest);
+
+    for (const perm of perms) {
+      result.add(char + perm);
+    }
+  }
+
+  return result;
+}
+
+// Tests
+let desc = 'empty string';
+let input = '';
+let actual = getPermutations(input);
+let expected = new Set(['']);
+assert(isSetsEqual(actual, expected), desc);
+
+desc = 'one character string';
+input = 'a';
+actual = getPermutations(input);
+expected = new Set(['a']);
+assert(isSetsEqual(actual, expected), desc);
+
+desc = 'two character string';
+input = 'ab';
+actual = getPermutations(input);
+expected = new Set(['ab', 'ba']);
+assert(isSetsEqual(actual, expected), desc);
+
+desc = 'three character string';
+input = 'abc';
+actual = getPermutations(input);
+expected = new Set(['abc', 'acb', 'bac', 'bca', 'cab', 'cba']);
+assert(isSetsEqual(actual, expected), desc);
+
+desc = 'four character string';
+input = 'abca';
+actual = getPermutations(input);
+expected = new Set([
+  'abca', 'abac', 'acba', 'acab', 'aabc', 'aacb', 'baca', 'baac', 'bcaa',
+  'bcaa', 'baac', 'baca', 'caba', 'caab', 'cbaa', 'cbaa', 'caab', 'caba',
+  'aabc', 'aacb', 'abac', 'abca', 'acab', 'acba'
+]);
+assert(isSetsEqual(actual, expected), desc);
+
+function isSetsEqual(as, bs) {
+  if (as.size !== bs.size) {
+    return false;
+  }
+  for (let a of as) {
+    if (!bs.has(a)) return false;
+  }
+  return true;
+}
+
+function assert(condition, desc) {
+  if (condition) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/reverse-string-in-place.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/reverse-string-in-place.ts
@ -0,0 +1,13 @@
+// Reverse array of characters, `xs`, mutatively.
+function reverse(xs: Array<string>) {
+  let i: number = 0;
+  let j: number = xs.length - 1;
+
+  while (i < j) {
+    let tmp = xs[i];
+    xs[i] = xs[j]
+    xs[j] = tmp
+    i += 1
+    j -= 1
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/reverse-words.py
+++ b/users/wpcarro/scratch/deepmind/part_two/reverse-words.py
@ -0,0 +1,74 @@
+import unittest
+
+
+def reverse(xs, i, j):
+    """Reverse array of characters, xs, in-place."""
+    while i < j:
+        xs[i], xs[j] = xs[j], xs[i]
+        i += 1
+        j -= 1
+
+
+def reverse_words(xs):
+    punctuation = None
+    if len(xs) > 0 and xs[-1] in ".?!":
+        punctuation = xs.pop()
+    reverse(xs, 0, len(xs) - 1)
+    i = 0
+    j = i
+    while j < len(xs):
+        while j < len(xs) and xs[j] != ' ':
+            j += 1
+        reverse(xs, i, j - 1)
+        j += 1
+        i = j
+    if punctuation:
+        xs.append(punctuation)
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_one_word(self):
+        message = list('vault')
+        reverse_words(message)
+        expected = list('vault')
+        self.assertEqual(message, expected)
+
+    def test_two_words(self):
+        message = list('thief cake')
+        reverse_words(message)
+        expected = list('cake thief')
+        self.assertEqual(message, expected)
+
+    def test_three_words(self):
+        message = list('one another get')
+        reverse_words(message)
+        expected = list('get another one')
+        self.assertEqual(message, expected)
+
+    def test_multiple_words_same_length(self):
+        message = list('rat the ate cat the')
+        reverse_words(message)
+        expected = list('the cat ate the rat')
+        self.assertEqual(message, expected)
+
+    def test_multiple_words_different_lengths(self):
+        message = list('yummy is cake bundt chocolate')
+        reverse_words(message)
+        expected = list('chocolate bundt cake is yummy')
+        self.assertEqual(message, expected)
+
+    def test_empty_string(self):
+        message = list('')
+        reverse_words(message)
+        expected = list('')
+        self.assertEqual(message, expected)
+
+    def test_bonus_support_punctuation(self):
+        message = list('yummy is cake bundt chocolate this!')
+        reverse_words(message)
+        expected = list('this chocolate bundt cake is yummy!')
+        self.assertEqual(message, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/second-largest-item-in-bst.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/second-largest-item-in-bst.ts
@ -0,0 +1,219 @@
+/*******************************************************************************
+ * Setup
+ ******************************************************************************/
+
+interface BinaryTreeNode {
+  value: number;
+  left: BinaryTreeNode;
+  right: BinaryTreeNode;
+}
+
+class BinaryTreeNode {
+  constructor(value: number) {
+    this.value = value;
+    this.left  = null;
+    this.right = null;
+  }
+
+  insertLeft(value: number): BinaryTreeNode {
+    this.left = new BinaryTreeNode(value);
+    return this.left;
+  }
+
+  insertRight(value: number): BinaryTreeNode {
+    this.right = new BinaryTreeNode(value);
+    return this.right;
+  }
+}
+
+/*******************************************************************************
+ * First solution
+ ******************************************************************************/
+
+/**
+ * I first solved this problem using O(n) space and O(n*log(n))
+ * time. InterviewCake informs me that we can improve both the time and the
+ * space performance.
+ */
+function findSecondLargest_first(node: BinaryTreeNode): number {
+  const stack: Array<BinaryTreeNode> = [];
+  const xs: Array<number> = [];
+  stack.push(node);
+
+  while (stack.length > 0) {
+    const node = stack.pop()
+
+    xs.push(node.value);
+
+    if (node.left) {
+      stack.push(node.left);
+    }
+    if (node.right) {
+      stack.push(node.right);
+    }
+  }
+
+  xs.sort();
+
+  if (xs.length < 2) {
+    throw new Error('Cannot find the second largest element in a BST with fewer than two elements.');
+  } else {
+    return xs[xs.length - 2];
+  }
+}
+
+/*******************************************************************************
+ * Second solution
+ ******************************************************************************/
+
+/**
+ * My second solution accumulates a list of the values in the tree using an
+ * in-order traversal. This reduces the runtime costs from O(n*log(n)) from the
+ * previous solution to O(n). The memory cost is still O(n), which InterviewCake
+ * informs me can be reduced to O(1).
+ */
+function findSecondLargest_second(node: BinaryTreeNode): number {
+  const xs: Array<number> = accumulateInorder(node);
+
+  if (xs.length < 2) {
+    throw new Error('Cannot find the second largest element in a BST with fewer than two elements.');
+  } else {
+    return xs[xs.length - 2];
+  }
+}
+
+/**
+ * Returns an array containing the values of the tree, `node`, sorted in-order
+ * (i.e. from smallest-to-largest).
+ */
+function accumulateInorder(node: BinaryTreeNode): Array<number> {
+  let result = [];
+
+  if (node.left) {
+    result = result.concat(accumulateInorder(node.left));
+  }
+  result.push(node.value)
+  if (node.right) {
+    result = result.concat(accumulateInorder(node.right));
+  }
+
+  return result;
+}
+
+/*******************************************************************************
+ * Third solution
+ ******************************************************************************/
+
+/**
+ * Returns the largest number in a BST.
+ */
+function findLargest(node: BinaryTreeNode): number {
+  let curr: BinaryTreeNode = node;
+
+  while (curr.right) {
+    curr = curr.right;
+  }
+
+  return curr.value;
+}
+
+/**
+ * Returns the second largest number in a BST
+ */
+function findSecondLargest(node: BinaryTreeNode): number {
+  let curr = node;
+  let parent = null;
+
+  while (curr.right) {
+    parent = curr;
+    curr = curr.right
+  }
+
+  if (curr.left) {
+    return findLargest(curr.left);
+  }
+  else {
+    return parent.value;
+  }
+}
+
+
+// Tests
+let desc = 'full tree';
+let treeRoot = new BinaryTreeNode(50);
+let leftNode = treeRoot.insertLeft(30);
+leftNode.insertLeft(10);
+leftNode.insertRight(40);
+let rightNode = treeRoot.insertRight(70);
+rightNode.insertLeft(60);
+rightNode.insertRight(80);
+assertEquals(findSecondLargest(treeRoot), 70, desc);
+
+desc = 'largest has a left child';
+treeRoot = new BinaryTreeNode(50);
+leftNode = treeRoot.insertLeft(30);
+leftNode.insertLeft(10);
+leftNode.insertRight(40);
+rightNode = treeRoot.insertRight(70);
+rightNode.insertLeft(60);
+assertEquals(findSecondLargest(treeRoot), 60, desc);
+
+desc = 'largest has a left subtree';
+treeRoot = new BinaryTreeNode(50);
+leftNode = treeRoot.insertLeft(30);
+leftNode.insertLeft(10);
+leftNode.insertRight(40);
+rightNode = treeRoot.insertRight(70);
+leftNode = rightNode.insertLeft(60);
+leftNode.insertRight(65);
+leftNode = leftNode.insertLeft(55);
+leftNode.insertRight(58);
+assertEquals(findSecondLargest(treeRoot), 65, desc);
+
+desc = 'second largest is root node';
+treeRoot = new BinaryTreeNode(50);
+leftNode = treeRoot.insertLeft(30);
+leftNode.insertLeft(10);
+leftNode.insertRight(40);
+rightNode = treeRoot.insertRight(70);
+assertEquals(findSecondLargest(treeRoot), 50, desc);
+
+desc = 'descending linked list';
+treeRoot = new BinaryTreeNode(50);
+leftNode = treeRoot.insertLeft(40);
+leftNode = leftNode.insertLeft(30);
+leftNode = leftNode.insertLeft(20);
+leftNode = leftNode.insertLeft(10);
+assertEquals(findSecondLargest(treeRoot), 40, desc);
+
+desc = 'ascending linked list';
+treeRoot = new BinaryTreeNode(50);
+rightNode = treeRoot.insertRight(60);
+rightNode = rightNode.insertRight(70);
+rightNode = rightNode.insertRight(80);
+assertEquals(findSecondLargest(treeRoot), 70, desc);
+
+desc = 'one node tree';
+treeRoot = new BinaryTreeNode(50);
+assertThrowsError(() => findSecondLargest(treeRoot), desc);
+
+desc = 'when tree is empty';
+treeRoot = null;
+assertThrowsError(() => findSecondLargest(treeRoot), desc);
+
+function assertEquals(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`)
+  }
+}
+
+function assertThrowsError(func, desc) {
+  try {
+    func();
+    console.log(`${desc} ... FAIL`);
+  } catch (e) {
+    console.log(`${desc} ... PASS`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/shell.nix
+++ b/users/wpcarro/scratch/deepmind/part_two/shell.nix
@ -0,0 +1,11 @@
+let
+  briefcase = import <briefcase> {};
+  pkgs = briefcase.third_party.pkgs;
+in pkgs.mkShell {
+  buildInputs = with pkgs; [
+    nodejs
+    python3
+    go
+    goimports
+  ];
+}
--- a/users/wpcarro/scratch/deepmind/part_two/shuffle.py
+++ b/users/wpcarro/scratch/deepmind/part_two/shuffle.py
@ -0,0 +1,20 @@
+import random
+
+
+def get_random(floor, ceiling):
+    return random.randrange(floor, ceiling + 1)
+
+
+def shuffle(xs):
+    n = len(xs)
+    for i in range(n - 1):
+        j = get_random(i + 1, n - 1)
+        xs[i], xs[j] = xs[j], xs[i]
+
+
+sample_list = [1, 2, 3, 4, 5]
+print('Sample list:', sample_list)
+
+print('Shuffling sample list...')
+shuffle(sample_list)
+print(sample_list)
--- a/users/wpcarro/scratch/deepmind/part_two/stock-price.py
+++ b/users/wpcarro/scratch/deepmind/part_two/stock-price.py
@ -0,0 +1,54 @@
+import unittest
+
+
+def get_max_profit(xs):
+    if len(xs) < 2:
+        raise Exception('Can only trade with two or more ticker values.')
+    lowest_buy = xs[0]
+    max_profit = None
+    for x in xs[1:]:
+        if not max_profit:
+            max_profit = x - lowest_buy
+        else:
+            max_profit = max(max_profit, x - lowest_buy)
+        lowest_buy = min(lowest_buy, x)
+    return max_profit
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_price_goes_up_then_down(self):
+        actual = get_max_profit([1, 5, 3, 2])
+        expected = 4
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_down_then_up(self):
+        actual = get_max_profit([7, 2, 8, 9])
+        expected = 7
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_up_all_day(self):
+        actual = get_max_profit([1, 6, 7, 9])
+        expected = 8
+        self.assertEqual(actual, expected)
+
+    def test_price_goes_down_all_day(self):
+        actual = get_max_profit([9, 7, 4, 1])
+        expected = -2
+        self.assertEqual(actual, expected)
+
+    def test_price_stays_the_same_all_day(self):
+        actual = get_max_profit([1, 1, 1, 1])
+        expected = 0
+        self.assertEqual(actual, expected)
+
+    def test_error_with_empty_prices(self):
+        with self.assertRaises(Exception):
+            get_max_profit([])
+
+    def test_error_with_one_price(self):
+        with self.assertRaises(Exception):
+            get_max_profit([1])
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/todo.org
+++ b/users/wpcarro/scratch/deepmind/part_two/todo.org
@ -0,0 +1,77 @@
+* Array and string manipulation
+** DONE Merging Meeting Times
+** DONE Reverse String in Place
+** DONE Reverse Words
+** DONE Merge Sorted Arrays
+** DONE Cafe Order Checker
+* Hashing and hash tables
+** DONE Inflight Entertainment
+** DONE Permutation Palindrome
+** DONE Word Cloud Data
+** DONE Top Scores
+* Greedy Algorithms
+** DONE Apple Stocks
+** DONE Highest Product of 3
+** DONE Product of All Other Numbers
+** DONE Cafe Order Checker
+** DONE In-Place Shuffle
+* Sorting, searching, and logarithms
+** DONE Find Rotation Point
+** TODO Find Repeat, Space Edition
+** DONE Top Scores
+** DONE Merging Meeting Times
+* Trees and graphs
+** DONE Balanced Binary Tree
+** DONE Binary Search Tree Checker
+** DONE 2nd Largest Item in a Binary Search Tree
+** DONE Graph Coloring
+** DONE MeshMessage
+** DONE Find Repeat, Space Edition BEAST MODE
+* Dynamic programming and recursion
+** DONE Recursive String Permutations
+** DONE Compute nth Fibonacci Number
+** TODO Making Change
+** TODO The Cake Thief
+** DONE Balanced Binary Tree
+** DONE Binary Search Tree Checker
+** DONE 2nd Largest Item in a Binary Search Tree
+* Queues and stacks
+** TODO Largest Stack
+** TODO Implement A Queue With Two Stacks
+** TODO Parenthesis Matching
+** TODO Bracket Validator
+* Linked lists
+** DONE Delete Node
+** TODO Does This Linked List Have A Cycle?
+** TODO Reverse A Linked List
+** TODO Kth to Last Node in a Singly-Linked List
+** DONE Find Repeat, Space Edition BEAST MODE
+* System design
+** TODO URL Shortener
+** TODO MillionGazillion
+** TODO Find Duplicate Files
+* General programming
+** TODO Rectangular Love
+** TODO Temperature Tracker
+* Bit manipulation
+** TODO Binary Numbers
+** TODO The Stolen Breakfast Drone
+* Combinatorics, probability, and other math
+** TODO Which Appears Twice
+** TODO Find in Ordered Set
+** DONE In-Place Shuffle
+** TODO Simulate 5-sided die
+** TODO Simulate 7-sided die
+** TODO Two Egg Problem
+* JavaScript
+** TODO JavaScript Scope
+** TODO What's Wrong with This JavaScript?
+* Coding interview tips
+** TODO How The Coding Interview Works
+** TODO General Coding Interview Advice
+** TODO Impostor Syndrome
+** TODO Why You Hit Dead Ends
+** TODO Tips for Getting Unstuck
+** TODO The 24 Hours Before Your Interview
+** TODO Beating Behavioral Questions
+** TODO Managing Your Interview Timeline
--- a/users/wpcarro/scratch/deepmind/part_two/top-scores.py
+++ b/users/wpcarro/scratch/deepmind/part_two/top-scores.py
@ -0,0 +1,47 @@
+import unittest
+
+
+def sort_scores(xs, highest_possible_score):
+    result = []
+    buckets = [0] * highest_possible_score
+
+    for x in xs:
+        buckets[x - 1] += 1
+
+    for i in range(highest_possible_score - 1, -1, -1):
+        if buckets[i] > 0:
+            for _ in range(buckets[i]):
+                result.append(i + 1)
+
+    return result
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_no_scores(self):
+        actual = sort_scores([], 100)
+        expected = []
+        self.assertEqual(actual, expected)
+
+    def test_one_score(self):
+        actual = sort_scores([55], 100)
+        expected = [55]
+        self.assertEqual(actual, expected)
+
+    def test_two_scores(self):
+        actual = sort_scores([30, 60], 100)
+        expected = [60, 30]
+        self.assertEqual(actual, expected)
+
+    def test_many_scores(self):
+        actual = sort_scores([37, 89, 41, 65, 91, 53], 100)
+        expected = [91, 89, 65, 53, 41, 37]
+        self.assertEqual(actual, expected)
+
+    def test_repeated_scores(self):
+        actual = sort_scores([20, 10, 30, 30, 10, 20], 100)
+        expected = [30, 30, 20, 20, 10, 10]
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)
--- a/users/wpcarro/scratch/deepmind/part_two/top-scores.ts
+++ b/users/wpcarro/scratch/deepmind/part_two/top-scores.ts
@ -0,0 +1,57 @@
+function sortScores(xs: Array<number>, highest: number): Array<number> {
+  const counts: Array<number> = [];
+  const result: Array<number> = [];
+
+  // Initialize counts
+  for (let i = 0; i <= highest; i += 1) {
+    counts.push(0);
+  }
+
+  for (let i = 0; i < xs.length; i += 1) {
+    counts[xs[i]] += 1;
+  }
+
+  for (let i = highest; i >= 0; i -= 1) {
+    let count: number = counts[i];
+
+    for (let j = 0; j < count; j += 1) {
+      result.push(i);
+    }
+  }
+
+  return result;
+}
+
+// Tests
+let desc = "no scores";
+let actual = sortScores([], 100);
+let expected = [];
+assertEqual(JSON.stringify(actual), JSON.stringify(expected), desc);
+
+desc = "one score";
+actual = sortScores([55], 100);
+expected = [55];
+assertEqual(JSON.stringify(actual), JSON.stringify(expected), desc);
+
+desc = "two scores";
+actual = sortScores([30, 60], 100);
+expected = [60, 30];
+assertEqual(JSON.stringify(actual), JSON.stringify(expected), desc);
+
+desc = "many scores";
+actual = sortScores([37, 89, 41, 65, 91, 53], 100);
+expected = [91, 89, 65, 53, 41, 37];
+assertEqual(JSON.stringify(actual), JSON.stringify(expected), desc);
+
+desc = "repeated scores";
+actual = sortScores([20, 10, 30, 30, 10, 20], 100);
+expected = [30, 30, 20, 20, 10, 10];
+assertEqual(JSON.stringify(actual), JSON.stringify(expected), desc);
+
+function assertEqual(a, b, desc) {
+  if (a === b) {
+    console.log(`${desc} ... PASS`);
+  } else {
+    console.log(`${desc} ... FAIL: ${a} != ${b}`);
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/tsconfig.json
+++ b/users/wpcarro/scratch/deepmind/part_two/tsconfig.json
@ -0,0 +1,7 @@
+{
+  "compilerOptions": {
+    "downlevelIteration": true,
+    "target": "es5",
+    "lib": ["es6", "dom"]
+  }
+}
--- a/users/wpcarro/scratch/deepmind/part_two/word-cloud.py
+++ b/users/wpcarro/scratch/deepmind/part_two/word-cloud.py
@ -0,0 +1,79 @@
+import unittest
+import re
+from collections import Counter
+
+
+class WordCloudData(object):
+    def __init__(self, x):
+        x = x.replace('...', ' ').replace(' - ', ' ')
+        x = ''.join(c for c in x if c not in ',.!?;:')
+        self.words_to_counts = dict(
+            Counter(x.lower() for x in re.split(r'\s+', x)))
+
+
+# Tests
+class Test(unittest.TestCase):
+    def test_simple_sentence(self):
+        input = 'I like cake'
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {'i': 1, 'like': 1, 'cake': 1}
+        self.assertEqual(actual, expected)
+
+    def test_longer_sentence(self):
+        input = 'Chocolate cake for dinner and pound cake for dessert'
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {
+            'and': 1,
+            'pound': 1,
+            'for': 2,
+            'dessert': 1,
+            'chocolate': 1,
+            'dinner': 1,
+            'cake': 2,
+        }
+        self.assertEqual(actual, expected)
+
+    def test_punctuation(self):
+        input = 'Strawberry short cake? Yum!'
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {'cake': 1, 'strawberry': 1, 'short': 1, 'yum': 1}
+        self.assertEqual(actual, expected)
+
+    def test_hyphenated_words(self):
+        input = 'Dessert - mille-feuille cake'
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {'cake': 1, 'dessert': 1, 'mille-feuille': 1}
+        self.assertEqual(actual, expected)
+
+    def test_ellipses_between_words(self):
+        input = 'Mmm...mmm...decisions...decisions'
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {'mmm': 2, 'decisions': 2}
+        self.assertEqual(actual, expected)
+
+    def test_apostrophes(self):
+        input = "Allie's Bakery: Sasha's Cakes"
+
+        word_cloud = WordCloudData(input)
+        actual = word_cloud.words_to_counts
+
+        expected = {"bakery": 1, "cakes": 1, "allie's": 1, "sasha's": 1}
+        self.assertEqual(actual, expected)
+
+
+unittest.main(verbosity=2)