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43 lines
1.1 KiB
Python
43 lines
1.1 KiB
Python
"""
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File: permutations_i.py
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Created Time: 2023-04-15
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Author: Krahets (krahets@163.com)
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"""
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import sys, os.path as osp
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sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
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from modules import *
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def backtrack(
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state: list[int], choices: list[int], selected: list[bool], res: list[list[int]]
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):
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"""回溯算法：全排列 I"""
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# 当状态长度等于元素数量时，记录解
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if len(state) == len(choices):
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res.append(list(state))
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return
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# 遍历所有选择
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for i, choice in enumerate(choices):
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# 剪枝：不允许重复选择元素
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if not selected[i]:
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# 尝试
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selected[i] = True # 做出选择
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state.append(choice) # 更新状态
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backtrack(state, choices, selected, res)
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# 回退
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selected[i] = False # 撤销选择
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state.pop() # 恢复到之前的状态
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"""Driver Code"""
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if __name__ == "__main__":
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nums = [1, 2, 3]
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res = []
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# 回溯算法
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backtrack(state=[], choices=nums, selected=[False] * len(nums), res=res)
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print(f"输入数组 nums = {nums}")
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print(f"所有排列 res = {res}")
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