111 lines
3.1 KiB
Python
111 lines
3.1 KiB
Python
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import unittest
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from collections import deque
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# While this function solves the problem, it uses O(n) space since we're storing
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# all of the less-thans and greater-thans.
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def is_binary_search_tree_first_attempt(root):
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q = deque()
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q.append((set(), set(), root))
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while q:
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lts, gts, node = q.popleft()
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if not all([node.value < lt for lt in lts]):
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return False
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if not all([node.value > gt for gt in gts]):
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return False
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if node.left:
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q.append((lts | {node.value}, gts, node.left))
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if node.right:
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q.append((lts, gts | {node.value}, node.right))
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return True
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# While I did not originally solve this problem this way, when I learned that I
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# could condense the space of my solution's runtime, I wrote this.
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def is_binary_search_tree(root):
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q = deque()
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q.append((None, None, root))
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while q:
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lt, gt, node = q.popleft()
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if not lt is None and node.value >= lt:
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return False
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if not gt is None and node.value <= gt:
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return False
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if node.left:
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q.append((node.value, gt, node.left))
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if node.right:
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q.append((lt, node.value, node.right))
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return True
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# Tests
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class Test(unittest.TestCase):
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class BinaryTreeNode(object):
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def __init__(self, value):
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self.value = value
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self.left = None
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self.right = None
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def insert_left(self, value):
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self.left = Test.BinaryTreeNode(value)
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return self.left
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def insert_right(self, value):
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self.right = Test.BinaryTreeNode(value)
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return self.right
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def test_valid_full_tree(self):
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tree = Test.BinaryTreeNode(50)
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left = tree.insert_left(30)
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right = tree.insert_right(70)
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left.insert_left(10)
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left.insert_right(40)
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right.insert_left(60)
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right.insert_right(80)
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result = is_binary_search_tree(tree)
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self.assertTrue(result)
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def test_both_subtrees_valid(self):
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tree = Test.BinaryTreeNode(50)
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left = tree.insert_left(30)
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right = tree.insert_right(80)
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left.insert_left(20)
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left.insert_right(60)
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right.insert_left(70)
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right.insert_right(90)
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result = is_binary_search_tree(tree)
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self.assertFalse(result)
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def test_descending_linked_list(self):
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tree = Test.BinaryTreeNode(50)
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left = tree.insert_left(40)
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left_left = left.insert_left(30)
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left_left_left = left_left.insert_left(20)
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left_left_left.insert_left(10)
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result = is_binary_search_tree(tree)
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self.assertTrue(result)
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def test_out_of_order_linked_list(self):
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tree = Test.BinaryTreeNode(50)
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right = tree.insert_right(70)
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right_right = right.insert_right(60)
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right_right.insert_right(80)
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result = is_binary_search_tree(tree)
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self.assertFalse(result)
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def test_one_node_tree(self):
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tree = Test.BinaryTreeNode(50)
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result = is_binary_search_tree(tree)
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self.assertTrue(result)
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unittest.main(verbosity=2)
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