29 lines
1.0 KiB
Python
29 lines
1.0 KiB
Python
|
"""
|
||
|
|
Find all the permutations of a given string
|
||
|
|
Sample input: 'ABC'
|
||
|
|
Expected output: ['ABC', 'ACB', 'BAC', 'BCA', 'CAB', 'CBA']
|
||
|
|
Description: The algorithm is recursive. In each recursion, each element of the string (left) is removed and added to the beginning (head). This process is repeated until left is empty.
|
||
|
|
Time complexity: (n!)
|
||
|
|
"""
|
||
|
|
|
||
|
|
def permutation(head, left, permutations):
|
||
|
|
if len(left) == 0:
|
||
|
|
permutations.append(head)
|
||
|
|
else:
|
||
|
|
for i in range(len(left)):
|
||
|
|
permutation(head+left[i], left[:i]+left[i+1:], permutations)
|
||
|
|
|
||
|
|
def find_all_permutations(string):
|
||
|
|
permutations = []
|
||
|
|
permutation('', string, permutations)
|
||
|
|
return permutations
|
||
|
|
|
||
|
|
if __name__ == "__main__":
|
||
|
|
input = 'ABC'
|
||
|
|
output = find_all_permutations(input)
|
||
|
|
|
||
|
|
expected = ['ABC', 'ACB', 'BAC', 'BCA', 'CAB', 'CBA']
|
||
|
|
assert len(output) == len(expected), f"Expected 6 permutations, got: {len(expected)}"
|
||
|
|
for perm in expected:
|
||
|
|
assert perm in output, f"Expected permutation {perm} to be in output, missing"
|