Leetcode 129. Sum Root to Leaf Numbers

https://leetcode.com/problems/sum-root-to-leaf-numbers/description/

class Solution {public:    // int ans;    int sumNumbers(TreeNode* root) {        if (!root) return 0;        if (!root->left && !root->right) return root->val;        int ans = 0;        if (root->left) ans += dfs(root->left, root->val);        if (root->right) ans += dfs(root->right, root->val);        return ans;    }            int dfs(TreeNode* root, int v) {        if (!root) return v;        int cur_v =  v*10 + root->val;        if (!root->left && !root->right) {            return cur_v;        }        int ret = 0;        if (root->left) ret += dfs(root->left, cur_v);        if (root->right) ret += dfs(root->right, cur_v);        return ret;    }    };