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49 lines
1.3 KiB
Python
49 lines
1.3 KiB
Python
def permute_recursive(nums: list[int]) -> list[list[int]]:
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"""
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Return all permutations.
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>>> permute_recursive([1, 2, 3])
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[[3, 2, 1], [2, 3, 1], [1, 3, 2], [3, 1, 2], [2, 1, 3], [1, 2, 3]]
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"""
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result: list[list[int]] = []
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if len(nums) == 0:
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return [[]]
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for _ in range(len(nums)):
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n = nums.pop(0)
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permutations = permute_recursive(nums.copy())
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for perm in permutations:
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perm.append(n)
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result.extend(permutations)
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nums.append(n)
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return result
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def permute_backtrack(nums: list[int]) -> list[list[int]]:
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"""
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Return all permutations of the given list.
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>>> permute_backtrack([1, 2, 3])
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[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 2, 1], [3, 1, 2]]
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"""
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def backtrack(start: int) -> None:
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if start == len(nums) - 1:
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output.append(nums[:])
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else:
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for i in range(start, len(nums)):
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nums[start], nums[i] = nums[i], nums[start]
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backtrack(start + 1)
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nums[start], nums[i] = nums[i], nums[start] # backtrack
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output: list[list[int]] = []
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backtrack(0)
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return output
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if __name__ == "__main__":
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import doctest
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result = permute_backtrack([1, 2, 3])
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print(result)
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doctest.testmod()
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