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.

这个题目简单，一次过。DFS就行，我用了个前序遍历，代码：

 1     int sumNumbers(TreeNode *root) {
 2         if(!root) return 0;
 3         int result=0,t=0;
 4         preOrder(root,&result,&t);
 5         return result;
 6     }
 7     void preOrder(TreeNode* root,int* sum,int* curSum){
 8         *curSum=*curSum*10+root->val;
 9         if(!root->left&&!root->right){//leaf node
10             *sum+=*curSum;
11             return;
12         }
13         if(root->left){
14             preOrder(root->left,sum,curSum);
15             *curSum/=10;
16         }
17         if(root->right){
18             preOrder(root->right,sum,curSum);
19             *curSum/=10;
20         }
21     }