[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.

Analysis:

/**
 * 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 helper(TreeNode *root, int& sum, int s)
    {
        if (root == NULL)
            return;
        else if (root->left == NULL && root->right == NULL)
            sum += (s*10 + root->val);
        else
        {
            helper(root->left, sum, s*10 + root->val);
            helper(root->right, sum, s*10 + root->val);
        }    
    }
    
    int sumNumbers(TreeNode *root) {
        int sum = 0;
        helper(root, sum, 0);
        
        return sum;
    }
};