leetcode-Sum Root to Leaf Numbers

Difficulty: Medium

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.

<span style="font-size:12px;">/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    int sum=0;
    void helper(TreeNode *root,string path){
        if(!root->left&&!root->right){
            sum+=stoi(path+to_string(root->val));
        }
        if(root->left)
            helper(root->left, path+to_string(root->val));
        if(root->right)
            helper(root->right,path+to_string(root->val));    
    }

public:
    int sumNumbers(TreeNode* root) {
        if(!root)
            return 0;
        string path;    
        helper(root,path);
        return sum;
    }
};</span>