# 143. Reorder List

## Medium

***

You are given the head of a singly linked-list. The list can be represented as:

```
L0 → L1 → … → Ln - 1 → Ln
```

*Reorder the list to be on the following form:*

```
L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …
```

You may not modify the values in the list's nodes. Only nodes themselves may be changed.

 

**Example 1:**

![](https://assets.leetcode.com/uploads/2021/03/04/reorder1linked-list.jpg)

```
Input: head = [1,2,3,4]
Output: [1,4,2,3]
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/03/09/reorder2-linked-list.jpg)

```
Input: head = [1,2,3,4,5]
Output: [1,5,2,4,3]
```

 

**Constraints:**

* The number of nodes in the list is in the range `[1, 5 * 104]`.
* `1 <= Node.val <= 1000`