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Java-based LeetCode algorithm problem solutions, regularly updated
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`