77 lines
2.2 KiB
C++
77 lines
2.2 KiB
C++
|
/**
|
||
|
|
* File: preorder_traversal_iii_template.cpp
|
||
|
|
* Created Time: 2023-04-16
|
||
|
|
* Author: krahets (krahets@163.com)
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include "../utils/common.hpp"
|
||
|
|
|
||
|
|
/* 判断当前状态是否为解 */
|
||
|
|
bool isSolution(vector<TreeNode *> &state) {
|
||
|
|
return !state.empty() && state.back()->val == 7;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 记录解 */
|
||
|
|
void recordSolution(vector<TreeNode *> &state, vector<vector<TreeNode *>> &res) {
|
||
|
|
res.push_back(state);
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 判断在当前状态下，该选择是否合法 */
|
||
|
|
bool isValid(vector<TreeNode *> &state, TreeNode *choice) {
|
||
|
|
return choice != nullptr && choice->val != 3;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 更新状态 */
|
||
|
|
void makeChoice(vector<TreeNode *> &state, TreeNode *choice) {
|
||
|
|
state.push_back(choice);
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 恢复状态 */
|
||
|
|
void undoChoice(vector<TreeNode *> &state, TreeNode *choice) {
|
||
|
|
state.pop_back();
|
||
|
|
}
|
||
|
|
|
||
|
|
/* 回溯算法：例题三 */
|
||
|
|
void backtrack(vector<TreeNode *> &state, vector<TreeNode *> &choices, vector<vector<TreeNode *>> &res) {
|
||
|
|
// 检查是否为解
|
||
|
|
if (isSolution(state)) {
|
||
|
|
// 记录解
|
||
|
|
recordSolution(state, res);
|
||
|
|
}
|
||
|
|
// 遍历所有选择
|
||
|
|
for (TreeNode *choice : choices) {
|
||
|
|
// 剪枝：检查选择是否合法
|
||
|
|
if (isValid(state, choice)) {
|
||
|
|
// 尝试：做出选择，更新状态
|
||
|
|
makeChoice(state, choice);
|
||
|
|
// 进行下一轮选择
|
||
|
|
vector<TreeNode *> nextChoices{choice->left, choice->right};
|
||
|
|
backtrack(state, nextChoices, res);
|
||
|
|
// 回退：撤销选择，恢复到之前的状态
|
||
|
|
undoChoice(state, choice);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Driver Code */
|
||
|
|
int main() {
|
||
|
|
TreeNode *root = vectorToTree(vector<int>{1, 7, 3, 4, 5, 6, 7});
|
||
|
|
cout << "\n初始化二叉树" << endl;
|
||
|
|
printTree(root);
|
||
|
|
|
||
|
|
// 回溯算法
|
||
|
|
vector<TreeNode *> state;
|
||
|
|
vector<TreeNode *> choices = {root};
|
||
|
|
vector<vector<TreeNode *>> res;
|
||
|
|
backtrack(state, choices, res);
|
||
|
|
|
||
|
|
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;
|
||
|
|
for (vector<TreeNode *> &path : res) {
|
||
|
|
vector<int> vals;
|
||
|
|
for (TreeNode *node : path) {
|
||
|
|
vals.push_back(node->val);
|
||
|
|
}
|
||
|
|
printVector(vals);
|
||
|
|
}
|
||
|
|
}
|