[LeetCode129]Sum Root to Leaf Numbers

题目：

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.

分类：Tree DFS

代码：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int sumNumbers(TreeNode* root) {
13         return DFS(root,0);
14     }
15     
16     int DFS(TreeNode* root, int sum)
17     {
18         if(!root)
19             return 0;
20         int newSum = sum * 10 + root->val;
21         if(!root->left && !root->right)
22             return newSum;
23         return DFS(root->left,newSum) + DFS(root->right,newSum);
24     }
25 };