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docs/notes/36. 二叉搜索树与双向链表.md

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+# 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)
+
+## 题目描述
+
+输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。
+
+<img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/05a08f2e-9914-4a77-92ef-aebeaecf4f66.jpg" width="400"/>
+
+## 解题思路
+
+```java
+private TreeNode pre = null;
+private TreeNode head = null;
+
+public TreeNode Convert(TreeNode root) {
+    inOrder(root);
+    return head;
+}
+
+private void inOrder(TreeNode node) {
+    if (node == null)
+        return;
+    inOrder(node.left);
+    node.left = pre;
+    if (pre != null)
+        pre.right = node;
+    pre = node;
+    if (head == null)
+        head = node;
+    inOrder(node.right);
+}
+```