/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int pathSum(TreeNode* root, int sum) {
if (root == NULL) return 0;
return dfs(root, sum) + pathSum(root->left, sum) + pathSum(root->right, sum);
}
int dfs(TreeNode* node, int sum) {
int res = 0;
if (node == NULL) return res;
if (sum == node->val) res++;
res += dfs(node->left, sum - node->val);
res += dfs(node->right, sum - node->val);
return res;
}
};