【leetcode】Sum Root to Leaf Numbers

Question：

Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path1->2->3which represents the number123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path1->2represents the number12.
The root-to-leaf path1->3represents the number13.

Return the sum = 12 + 13 =25.

Anwser 1：

/**
 * 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 calSum(TreeNode *root, int val, int &sum){
        if(root == NULL){
            return;
        }
        
        if(root->left == NULL && root->right == NULL){
            sum += root->val + val * 10;
            return;
        }
        
        calSum(root->left, val * 10 + root->val, sum);
        calSum(root->right, val * 10 + root->val, sum);
    }
    
    int sumNumbers(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int sum = 0;
        
        calSum(root, 0, sum);
        
        return sum;
    }
};