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 = 0;
        sumNumbersSub(root, 0, 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);
    }
    
};