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：

    int sumNumbers(TreeNode *root) {
        if(!root) return 0;
        int result=0,t=0;
        preOrder(root,&result,&t);
        return result;
    }
    void preOrder(TreeNode* root,int* sum,int* curSum){
        *curSum=*curSum*10+root->val;
        if(!root->left&&!root->right){//leaf node
            *sum+=*curSum;
            return;
        }
        if(root->left){
            preOrder(root->left,sum,curSum);
            *curSum/=10;
        }
        if(root->right){
            preOrder(root->right,sum,curSum);
            *curSum/=10;
        }
    }