> For the complete documentation index, see [llms.txt](https://mabuxi.gitbook.io/mabuxi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mabuxi.gitbook.io/mabuxi/leetcode-summary/linkedlist/fast-and-slow-pointer.md).

# Fast and Slow pointer

## 经典题目

[*109 Convert Sorted List to Binary Search Tree*](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/)

```
一般用Fast and Slow pointers 来找中点。

这个时候，有两种写法。
第一种
while(fast != null && fast.next != null) {
    fast = fast.next.next;
    slow = slow.next;
}

第二种
while(fast.next != null && fast.next.next != null) {
    fast = fast.next.next;
    slow = slow.next;
}

对于list包含奇数个node的情况，上面两种slow pointer最终都指向中间那个数，比如1 -> 2 -> 3 -> null，slow -> 2
对于list包含偶数个node的情况，比如1 -> 2 -> 3 -> 4 -> null，第一种情况slow -> 3，第二种slow -> 2
```