image.png

思路：回溯

  • cur_path 记录当前路径中的总和，如果在叶子节点上出现了cur_sum == target_sum，就将cur_path放到fit_path当中。否则就进行回溯操作。
  • 回溯的“回”如何实现？cur_path.pop_back()
  • image.png

代码：

  1. /**
  2.  * Definition for a binary tree node.
  3.  * struct TreeNode {
  4.  *     int val;
  5.  *     TreeNode *left;
  6.  *     TreeNode *right;
  7.  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
  8.  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  9.  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  10.  * };
  11.  */
  12. class Solution {
  13. public:
  14.     vector<vector<int>> fit_path;
  15.     vector<int> cur_path;
  17.     void traceBack(TreeNode* root, int pre_sum, int targetSum) {
  18.         if (!root) {
  19.             return;
  20.         }
  22.         int cur_sum = pre_sum + root->val;
  23.         cur_path.push_back(root->val);
  24.         if (!root->left && !root->right) {
  25.             if (cur_sum == targetSum) {
  26.                 fit_path.push_back(cur_path);
  27.             }
  28.         }
  29.         traceBack(root->left, cur_sum, targetSum);
  30.         traceBack(root->right, cur_sum, targetSum);
  32.         // 回溯的“回”操作
  33.         cur_path.pop_back();
  35.     }
  36.     vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
  37.         traceBack(root, 0, targetSum);
  38.         return fit_path;
  39.     }
  40. };