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* Retranslate the complete English edition from Simplified Chinese * Polish three English explanations after reader-focused review
47 lines
1.4 KiB
Python
47 lines
1.4 KiB
Python
"""
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File: permutations_ii.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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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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"""Backtracking: permutations II"""
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# Record a solution when the state length equals the number of elements
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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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# Iterate over all choices
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duplicated = set[int]()
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for i, choice in enumerate(choices):
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# Prune: do not reuse an element or choose the same value again at this depth
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if not selected[i] and choice not in duplicated:
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# Try: make a choice and update the state
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duplicated.add(choice) # Record the chosen value
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selected[i] = True
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state.append(choice)
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# Proceed to the next choice
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backtrack(state, choices, selected, res)
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# Backtrack: undo the choice and restore the previous state
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selected[i] = False
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state.pop()
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def permutations_ii(nums: list[int]) -> list[list[int]]:
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"""Permutations II"""
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res = []
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backtrack(state=[], choices=nums, selected=[False] * len(nums), res=res)
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return res
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"""Driver code"""
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if __name__ == "__main__":
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nums = [1, 2, 2]
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res = permutations_ii(nums)
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print(f"Input array nums = {nums}")
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print(f"All permutations: res = {res}")
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