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54 lines
1.3 KiB
54 lines
1.3 KiB
1 year ago
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/**
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* File: permutations_ii.dart
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* Created Time: 2023-08-10
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* 回溯算法：全排列 II */
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void backtrack(
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List<int> state,
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List<int> choices,
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List<bool> selected,
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List<List<int>> res,
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) {
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// 当状态长度等于元素数量时，记录解
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if (state.length == choices.length) {
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res.add(List.from(state));
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return;
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}
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// 遍历所有选择
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Set<int> duplicated = {};
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for (int i = 0; i < choices.length; i++) {
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int choice = choices[i];
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// 剪枝：不允许重复选择元素 且 不允许重复选择相等元素
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if (!selected[i] && !duplicated.contains(choice)) {
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// 尝试：做出选择，更新状态
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duplicated.add(choice); // 记录选择过的元素值
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selected[i] = true;
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state.add(choice);
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// 进行下一轮选择
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backtrack(state, choices, selected, res);
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// 回退：撤销选择，恢复到之前的状态
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selected[i] = false;
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state.removeLast();
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}
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}
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}
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/* 全排列 II */
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List<List<int>> permutationsII(List<int> nums) {
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List<List<int>> res = [];
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backtrack([], nums, List.filled(nums.length, false), res);
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return res;
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}
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/* Driver Code */
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void main() {
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List<int> nums = [1, 2, 2];
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List<List<int>> res = permutationsII(nums);
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print("输入数组 nums = $nums");
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print("所有排列 res = $res");
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}
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