129. Sum Root to Leaf Numbers LeetCode

题意：求二叉树所有根到叶子组成的数字之和。
题解：DFS。

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