LeetCode Problem : Sum Root to Leaf Numbers

Problem 

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.

Code

int sn_r(TreeNode *root,int parent)
{
    if(!root)
        return 0;
    int lsum = sn_r(root->left,10*parent + root->val);
    int rsum = sn_r(root->right,10*parent + root->val);
    if(lsum ==0 && rsum ==0)
        return (10*parent + root->val);
    return (lsum + rsum);
}
int sumNumbers(TreeNode *root) {
    // Note: The Solution object is instantiated only once and is reused by each test case.
    return sn_r(root,0);
}