leetcode-129 Sum Root to Leaf Numbers

<span style="font-family:Microsoft YaHei;font-size:14px;">/**
 * 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 sumNumbers(TreeNode *root) {
        if(root == NULL) return 0;
        int sum = 0;
        return helper(root,sum);
    }
    int helper(TreeNode *node,int sum){
        if(node->left == NULL && node->right == NULL)
            return sum * 10 + node->val;
        int val = 0;
        if(node->left != NULL)
           val += helper(node->left,sum * 10 + node->val);
        if(node->right != NULL)
           val += helper(node->right,sum * 10 + node->val);
        return val;
    }
};</span>