import unittest

def swap(arr, a, b):

arr[a], arr[b] = arr[b], arr[a]

def permutation(arr, length, offset, result):

if offset == length:

result.append(arr[:])

return

for i in range(offset, length):

swap(arr, i, offset)

permutation(arr, length, offset + 1, result)

swap(arr, i, offset)

class TestPermutation(unittest.TestCase):

def test(self):

arr = ['A', 'B', 'C']

result = []

permutation(arr, len(arr), 0, result)

self.assertEqual(

result,

[

['A', 'B', 'C'],

['A', 'C', 'B'],

['B', 'A', 'C'],

['B', 'C', 'A'],

['C', 'B', 'A'],

['C', 'A', 'B']

]

)

arr = ['1', '2', '3']

result = []

permutation(arr, len(arr), 0, result)

self.assertEqual(

result,

[

['1', '2', '3'],

['1', '3', '2'],

['2', '1', '3'],

['2', '3', '1'],

['3', '2', '1'],

['3', '1', '2']

]

)

if __name__ == '__main__':

unittest.TestCase()