[LeetCode] 129. 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.

class Solution {public:    int sumNumbers(TreeNode* root) {        int sum = 0;        sumNumbershelper(root, sum, 0);        return sum;    }private:    void sumNumbershelper(TreeNode *root, int &sum, int val) {        if (root == nullptr) return;        val = val * 10 + root->val;        if (root->left == nullptr && root->right == nullptr) {            sum += val;            return;        }        sumNumbershelper(root->left, sum, val);        sumNumbershelper(root->right, sum, val);    }};