[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.

Solution:

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