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50 lines
1.5 KiB
C++
50 lines
1.5 KiB
C++
/**
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* File: permutations_ii.cpp
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* Created Time: 2023-04-24
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* Author: Krahets (krahets@163.com)
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*/
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#include "../utils/common.hpp"
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/* 回溯算法：全排列 II */
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void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &selected, vector<vector<int>> &res) {
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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.size() == choices.size()) {
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res.push_back(state);
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return;
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}
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// 遍历所有选择
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unordered_set<int> duplicated;
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for (int i = 0; i < choices.size(); 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.find(choice) == duplicated.end()) {
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// 尝试
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duplicated.emplace(choice); // 记录选择过的元素值
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selected[i] = true; // 做出选择
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state.push_back(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_back(); // 恢复到之前的状态
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}
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}
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}
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/* Driver Code */
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int main() {
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vector<int> nums = {1, 1, 2};
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// 回溯算法
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vector<int> state;
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vector<bool> selected(nums.size(), false);
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vector<vector<int>> res;
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backtrack(state, nums, selected, res);
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cout << "输入数组 nums = ";
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printVector(nums);
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cout << "所有排列 res = ";
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printVectorMatrix(res);
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return 0;
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}
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