LeetCode算法题目：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.

分析：

简单的二叉树遍历，遍历时将自身的数值加入子节点。比如节点A的值是1，其左子节点的值是2，则将左子节点变为12。一旦遍历到叶子节点便将该叶子结点的值加入结果中。

代码：

/**
* 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) {
return dfs(root, 0);
}
private:
int dfs(TreeNode *root,int sum){
if(root==NULL) return 0;
if(root->left==NULL&&root->right==NULL)
return sum*10+root->val;
return dfs(root->left,sum*10+root->val)+dfs(root->right,sum*10+root->val);
}
};