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77 lines
2.2 KiB
C++
77 lines
2.2 KiB
C++
/**
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* File: preorder_traversal_iii_template.cpp
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* Created Time: 2023-04-16
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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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/* 判断当前状态是否为解 */
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bool isSolution(vector<TreeNode *> &state) {
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return !state.empty() && state.back()->val == 7;
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}
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/* 记录解 */
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void recordSolution(vector<TreeNode *> &state, vector<vector<TreeNode *>> &res) {
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res.push_back(state);
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}
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/* 判断在当前状态下，该选择是否合法 */
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bool isValid(vector<TreeNode *> &state, TreeNode *choice) {
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return choice != nullptr && choice->val != 3;
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}
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/* 更新状态 */
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void makeChoice(vector<TreeNode *> &state, TreeNode *choice) {
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state.push_back(choice);
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}
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/* 恢复状态 */
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void undoChoice(vector<TreeNode *> &state, TreeNode *choice) {
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state.pop_back();
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}
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/* 回溯算法：例题三 */
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void backtrack(vector<TreeNode *> &state, vector<TreeNode *> &choices, vector<vector<TreeNode *>> &res) {
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// 检查是否为解
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if (isSolution(state)) {
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// 记录解
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recordSolution(state, res);
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return;
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}
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// 遍历所有选择
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for (TreeNode *choice : choices) {
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// 剪枝：检查选择是否合法
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if (isValid(state, choice)) {
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// 尝试：做出选择，更新状态
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makeChoice(state, choice);
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// 进行下一轮选择
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vector<TreeNode *> nextChoices{choice->left, choice->right};
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backtrack(state, nextChoices, res);
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// 回退：撤销选择，恢复到之前的状态
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undoChoice(state, choice);
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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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TreeNode *root = vecToTree(vector<int>{1, 7, 3, 4, 5, 6, 7});
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cout << "\n初始化二叉树" << endl;
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printTree(root);
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// 回溯算法
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vector<TreeNode *> state;
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vector<TreeNode *> choices = {root};
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vector<vector<TreeNode *>> res;
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backtrack(state, choices, res);
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cout << "\n输出所有根节点到节点 7 的路径，要求路径中不包含值为 3 的节点" << endl;
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for (vector<TreeNode *> &path : res) {
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vector<int> vals;
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for (TreeNode *node : path) {
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vals.push_back(node->val);
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}
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printVector(vals);
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}
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}
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