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.

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