Complete string permutations problem

Solves an InterviewCake.com problem that returns all of the permutations of a
string input. The problem states that it's acceptable to assume that your input
string will not have repeated characters, which is why using a Set is
acceptable. I like this solution because it builds a permutations tree and then
assembles all of the permutations by doing a DFT over that tree.
This commit is contained in:
William Carroll 2020-01-22 10:09:46 +00:00
parent 64bd3f0303
commit bbea699f06

View file

@ -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)