leetcode-problemset/leetcode-cn/problem (English)/奇偶链表(English) [odd-even-linked-list].html

<p>Given the <code>head</code> of a singly linked list, group all the nodes with odd indices together followed by the nodes with even indices, and return <em>the reordered list</em>.</p>

<p>The <strong>first</strong> node is considered <strong>odd</strong>, and the <strong>second</strong> node is <strong>even</strong>, and so on.</p>

<p>Note that the relative order inside both the even and odd groups should remain as it was in the input.</p>

<p>You must solve the problem&nbsp;in <code>O(1)</code>&nbsp;extra space complexity and <code>O(n)</code> time complexity.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/oddeven-linked-list.jpg" style="width: 300px; height: 123px;" />
<pre>
<strong>Input:</strong> head = [1,2,3,4,5]
<strong>Output:</strong> [1,3,5,2,4]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/oddeven2-linked-list.jpg" style="width: 500px; height: 142px;" />
<pre>
<strong>Input:</strong> head = [2,1,3,5,6,4,7]
<strong>Output:</strong> [2,3,6,7,1,5,4]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the linked list is in the range <code>[0, 10<sup>4</sup>]</code>.</li>
	<li><code>-10<sup>6</sup> &lt;= Node.val &lt;= 10<sup>6</sup></code></li>
</ul>