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import unittest
################################################################################
# Answer
################################################################################
class Node(object):
def __init__(self, value, children=set()):
self.value = value
self.children = children
# treeify :: Char -> Set(Char) -> Node(Char)
def treeify(x, xs):
return Node(x, [treeify(c, xs - {c}) for c in xs])
# dft :: Node(Char) -> [String]
def dft(node):
result = []
s = []
s.append(('', node))
while s:
p, n = s.pop()
p += str(n.value)
if not n.children:
result.append(p)
else:
for c in n.children:
s.append((p, c))
return result
# main :: String -> Set(String)
def get_permutations(xs):
if xs == '':
return set([''])
ys = set(xs)
trees = []
for y in ys:
trees.append(treeify(y, ys - {y}))
result = set()
for t in trees:
for d in dft(t):
result.add(d)
return result
################################################################################
# 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)
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