golang刷leetcode 二叉搜索树与双向链表

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* left;
    Node* right;

    Node() {}

    Node(int _val) {
        val = _val;
        left = NULL;
        right = NULL;
    }

    Node(int _val, Node* _left, Node* _right) {
        val = _val;
        left = _left;
        right = _right;
    }
};
*/
class Solution {
public:
    Node* treeToDoublyList(Node* root) {
      if(root==NULL){
          return root;
      }
      dfs(root);
      head->left=pre;
      pre->right=head;
      return head;
    }
    Node *pre,*head;
   void dfs(Node*cur){
        if (cur==NULL){
             return ;
        }
        dfs(cur->left);
        if(pre==NULL){
            head=cur;
        }else{
            pre->right=cur;
            cur->left=pre;
        }
        pre=cur;
        dfs(cur->right);
    }
};