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47 lines
1.4 KiB
47 lines
1.4 KiB
"""
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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 algorithm: Permutation II"""
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# When the state length equals the number of elements, record the solution
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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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# Traverse all choices
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duplicated = set[int]()
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for i, choice in enumerate(choices):
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# Pruning: do not allow repeated selection of elements and do not allow repeated selection of equal elements
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if not selected[i] and choice not in duplicated:
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# Attempt: make a choice, update the state
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duplicated.add(choice) # Record selected element values
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selected[i] = True
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state.append(choice)
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# Proceed to the next round of selection
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backtrack(state, choices, selected, res)
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# Retract: undo the choice, restore to 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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"""Permutation 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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