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.

C++:
01 void sumNumbersHelper(TreeNode *root, int cur, int& result)
02 {
03    if(root==NULL)
04        return;
05    if((root->left==NULL)&&(root->right==NULL))
06    {
07        result+=cur*10+root->val;
08        return;
09    }
10    sumNumbersHelper(root->left, cur*10+root->val, result);
11    sumNumbersHelper(root->right, cur*10+root->val, result);
12 }
13 class Solution {
14 public:
15    int sumNumbers(TreeNode *root) {
16        // Start typing your C/C++ solution below
17        // DO NOT write int main() function
18        int result=0;
19        sumNumbersHelper(root,0,result);
20        return result;
21
22    }
23 };
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