# 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。

![](https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/05a08f2e-9914-4a77-92ef-aebeaecf4f66.jpg)\


## 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);
}
```