C++ 代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
   int pathcnt;
    int pathSum(TreeNode* root, int sum) {
        if(!root){
            return 0;
        }

         dfs(  root,   sum);
         pathSum(root->left,sum);
          pathSum(root->right,sum);
        return pathcnt;
    }
    void dfs(TreeNode* root, int sum){
        if(!root){
            return ;
        }

        if(sum==root->val){
            pathcnt++;

        }
        dfs( root->left,   sum-root->val);
        dfs( root->right,   sum-root->val);

    }

};