LeetCode : Path Sum III

Find the number of paths that sum to a given value.

The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).

The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.

Example:

root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8

  10 /  \5   -3

/ \ \
3 2 11
/ \ \
3 -2 1

Return 3. The paths that sum to 8 are:

1. 5 -> 3
2. 5 -> 2 -> 1
3. -3 -> 11

/** * 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 *root,int sum)    {        int res = 0;        if(root==NULL)           return res;        if(sum==root->val)            res++;        res+=dfs(root->left,sum-root->val);        res+=dfs(root->right,sum-root->val);        return res;    }};