# 876. Middle of the Linked List

**<font color=red>难度: Easy</font>**

## 刷题内容

> 原题连接

* https://leetcode.com/problems/middle-of-the-linked-list/

> 内容描述

```
Given a non-empty, singly linked list with head node head, return a middle node of linked list.

If there are two middle nodes, return the second middle node.

Example 1:

Input: [1,2,3,4,5]
Output: Node 3 from this list (Serialization: [3,4,5])
The returned node has value 3.  (The judge's serialization of this node is [3,4,5]).
Note that we returned a ListNode object ans, such that:
ans.val = 3, ans.next.val = 4, ans.next.next.val = 5, and ans.next.next.next = NULL.

Example 2:

Input: [1,2,3,4,5,6]
Output: Node 4 from this list (Serialization: [4,5,6])
Since the list has two middle nodes with values 3 and 4, we return the second one.
```

## 解题方案

> 思路 1
******- 时间复杂度: O(N)******- 空间复杂度: O(1)******

`fast`比`slow`遍历多一倍，当`fast`到底的时候，`slow`在中间。

beats 99.79%

```python
class Solution:
    def middleNode(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        fast = slow = head
        
        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            
        return slow
```
