leetcode-437.cpp

/**
 * 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==nullptr)
            return 0;
        return rootSum(root,sum)+pathSum(root->left,sum)+pathSum(root->right,sum);
    }

    int rootSum(TreeNode* root,int sum)
    {
        if(root==nullptr)
            return 0;
        return (root->val==sum)+rootSum(root->left,sum-root->val)+rootSum(root->right,sum-root->val);
    }
};