reorder-list

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Algorithms

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

<pre>
L0 &rarr; L1 &rarr; &hellip; &rarr; Ln - 1 &rarr; Ln
</pre>

Reorder the list to be on the following form:

<pre>
L0 &rarr; Ln &rarr; L1 &rarr; Ln - 1 &rarr; L2 &rarr; Ln - 2 &rarr; &hellip;
</pre>

You may not modify the values in the list&#39;s nodes. Only nodes themselves may be changed.

&nbsp;
Example 1:
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/04/reorder1linked-list.jpg" style="width: 422px; height: 222px;" />
<pre>
Input: head = [1,2,3,4]
Output: [1,4,2,3]
</pre>

Example 2:
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/09/reorder2-linked-list.jpg" style="width: 542px; height: 222px;" />
<pre>
Input: head = [1,2,3,4,5]
Output: [1,5,2,4,3]
</pre>

&nbsp;
Constraints:

<ul>
	<li>The number of nodes in the list is in the range <code>[1, 5 * 104]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 1000</code></li>
</ul>

reorderList

Reorder List

Delete the Middle Node of a Linked List

delete-the-middle-node-of-a-linked-list

删除链表的中间节点

Take K of Each Character From Left and Right

take-k-of-each-character-from-left-and-right

每种字符至少取 K 个

Stack

Recursion

Linked List

Two Pointers

给定一个单链表 <code>L</code> 的头节点 <code>head</code> ，单链表 <code>L</code> 表示为：

<pre>
L0 → L1 → … → Ln - 1 → Ln
</pre>

请将其重新排列后变为：

<pre>
L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …</pre>

不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。

&nbsp;

示例 1：

<img alt="" src="https://pic.leetcode-cn.com/1626420311-PkUiGI-image.png" style="width: 240px; " />

<pre>
输入：head = [1,2,3,4]
输出：[1,4,2,3]</pre>

示例 2：

<img alt="" src="https://pic.leetcode-cn.com/1626420320-YUiulT-image.png" style="width: 320px; " />

<pre>
输入：head = [1,2,3,4,5]
输出：[1,5,2,4,3]</pre>

&nbsp;

提示：

<ul>
	<li>链表的长度范围为 <code>[1, 5 * 104]</code></li>
	<li><code>1 &lt;= node.val &lt;= 1000</code></li>
</ul>