LeetCode 437. Path Sum III

/**
 * 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:
    
    //以Node为根节点的二叉树中，寻找包含Node 的路径
    int findPath(TreeNode* node ,int num){
        if( node == nullptr )
            return 0;
        int res = 0;
        if( node->val == num )
            res += 1;    
        res += findPath( node->left, num - node->val );
        res += findPath( node->right, num - node->val );    
        return res;
    }
    
    
    int pathSum(TreeNode* root, int sum) {
        if( root == nullptr )
            return 0;
        int res = findPath( root,sum );
        
        res += pathSum( root->left, sum );
        res += pathSum( root->right, sum );
        
        return res;
        
    }
};