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permutations.py
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34 lines (25 loc) · 842 Bytes
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from typing import List
def permutations(nums: List[int]) -> List[List[int]]:
ret_val: List[List[int]] = list()
def _permutations(curr_nums: List[int], taken: List[bool]):
if all(taken):
ret_val.append(curr_nums.copy())
else:
for idx, num in enumerate(nums):
if not taken[idx]:
taken[idx] = True
curr_nums.append(num)
_permutations(curr_nums, taken)
curr_nums.pop()
taken[idx] = False
_permutations(curr_nums=list(), taken=[False for _ in range(len(nums))])
return ret_val
assert permutations([1, 2]) == [[1, 2], [2, 1]]
assert permutations([1, 2, 3]) == [
[1, 2, 3],
[1, 3, 2],
[2, 1, 3],
[2, 3, 1],
[3, 1, 2],
[3, 2, 1],
]