Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

1   / \  2   3

 

The root-to-leaf path 1->2 represents the number 12.

The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

分析：DFS。代码如下：

class Solution {public:    int sumNumbers(TreeNode *root) {        int result = 0;        if(root == NULL) return result;        dfs(root, result, 0);        return result;    }        void dfs(TreeNode *root, int &result, int cur_sum){        cur_sum = cur_sum*10 + root->val;        if(root->left == NULL && root->right == NULL){            result += cur_sum;        }else{            if(root->left)                dfs(root->left, result, cur_sum);            if(root->right)                dfs(root->right, result, cur_sum);        }    }};