Update 36. 二叉搜索树与双向链表.md

题目链接改为力扣中的对应题目，题目描述和代码按该题的接口调整。

notes/36. 二叉搜索树与双向链表.md

@@ -1,6 +1,6 @@
 # 36. 二叉搜索树与双向链表
 
-[NowCoder](https://www.nowcoder.com/practice/947f6eb80d944a84850b0538bf0ec3a5?tpId=13&tqId=11179&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[Leetcode](https://leetcode.cn/problems/er-cha-sou-suo-shu-yu-shuang-xiang-lian-biao-lcof/)
 
 ## 题目描述
 
@@ -11,15 +11,21 @@
 ## 解题思路
 
 ```java
-private TreeNode pre = null;
-private TreeNode head = null;
+private Node pre = null;
+private Node head = null;
 
-public TreeNode Convert(TreeNode root) {
+public Node treeToDoublyList(Node root) {
+    if (root == null)
+        return null;
+    head = null;
+    pre = null;
     inOrder(root);
+    head.left = pre;
+    pre.right = head;
     return head;
 }
 
-private void inOrder(TreeNode node) {
+private void inOrder(Node node) {
     if (node == null)
         return;
     inOrder(node.left);