43 lines
1.1 KiB
Python
43 lines
1.1 KiB
Python
#!/usr/bin/python
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# -*- coding: UTF-8 -*-
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from typing import List
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permutations_list = [] # 全局变量，用于记录每个输出
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def permutations(nums: List, n: int, pick_count: int):
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"""
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从nums选取n个数的全排列
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回溯法，用一个栈记录当前路径信息
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当满足n==0时，说明栈中的数已足够，输出并终止遍历
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:param nums:
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:param n:
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:param pick_count:
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:return:
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"""
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if n == 0:
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print(permutations_list)
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else:
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for i in range(len(nums) - pick_count):
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permutations_list[pick_count] = nums[i]
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nums[i], nums[len(nums) - pick_count - 1] = nums[len(nums) - pick_count - 1], nums[i]
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permutations(nums, n-1, pick_count+1)
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nums[i], nums[len(nums) - pick_count - 1] = nums[len(nums) - pick_count - 1], nums[i]
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if __name__ == '__main__':
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nums = [1, 2, 3, 4]
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n = 3
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print('--- list ---')
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print(nums)
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print('\n--- pick num ---')
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print(n)
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print('\n--- permutation list ---')
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permutations_list = [0] * n
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permutations(nums, n, 0)
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