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.

/**

 * Definition for binary tree

 * 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 sum=0;

        calc(sum,0,root);

        return sum;

    }

    void calc(int& sum,int data,TreeNode* root)

    {

        if(root==NULL) return;

        

        data=data*10+root->val;

        if(root->left==NULL && root->right==NULL)

        {

            sum=sum+data;

            return;

        }

        calc(sum,data,root->left);

        calc(sum,data,root->right);

    }

};