LeetCode之“树”：Sum Root to Leaf Numbers

　　题目链接

　　题目要求：

　　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.

　　这道题利用深度优先搜索即可，具体程序（4ms）如下：

 /**
  * 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 sumNumbers(TreeNode* root) {
         int totalSum = ;
         sumNumbersSub(root, , totalSum);
         return totalSum;
     }

     void sumNumbersSub(TreeNode *tree, int sum, int &totalSum)
     {
         if(!tree)
             return;

         sum = sum * 10 + tree->val;
         if(!tree->left && !tree->right)
         {
             totalSum += sum;
             return;
         }

         sumNumbersSub(tree->left, sum, totalSum);
         sumNumbersSub(tree->right, sum, totalSum);
     }

 };