[LeetCode]Sum Root to Leaf Numbers

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.

思考：dfs。

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void DFS(TreeNode *root,int ans,int &sum)
    {
        if(root)
        {
            ans=ans*10+root->val;
            if(root->left==NULL&&root->right==NULL)
            {
                sum+=ans;
                ans=0;
            }
            DFS(root->left,ans,sum);
            DFS(root->right,ans,sum);
        }
    }
    int sumNumbers(TreeNode *root) {
        int ans=0;
        int sum=0;
        DFS(root,ans,sum);
        return sum;
    }
};