# 206：反转链表

给你单链表的头节点 `head` ，请你反转链表，并返回反转后的链表。

**示例 1：**

![img](https://assets.leetcode.com/uploads/2021/02/19/rev1ex1.jpg)

```
输入：head = [1,2,3,4,5]
输出：[5,4,3,2,1]
```

**示例 2：**

![img](https://assets.leetcode.com/uploads/2021/02/19/rev1ex2.jpg)

```
输入：head = [1,2]
输出：[2,1]
```

**示例 3：**

```
输入：head = []
输出：[]
```

**提示：**

* 链表中节点的数目范围是 `[0, 5000]`
* `-5000 <= Node.val <= 5000`

java：

```java
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode curr = head;
        while (curr != null) {
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
}
```


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