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| 1 | +<h2><a href="https://leetcode.com/problems/odd-even-linked-list">Odd Even Linked List</a></h2> <img src='https://img.shields.io/badge/Difficulty-Medium-orange' alt='Difficulty: Medium' /><hr><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> |
| 2 | + |
| 3 | +<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> |
| 4 | + |
| 5 | +<p>Note that the relative order inside both the even and odd groups should remain as it was in the input.</p> |
| 6 | + |
| 7 | +<p>You must solve the problem in <code>O(1)</code> extra space complexity and <code>O(n)</code> time complexity.</p> |
| 8 | + |
| 9 | +<p> </p> |
| 10 | +<p><strong class="example">Example 1:</strong></p> |
| 11 | +<img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/oddeven-linked-list.jpg" style="width: 300px; height: 123px;" /> |
| 12 | +<pre> |
| 13 | +<strong>Input:</strong> head = [1,2,3,4,5] |
| 14 | +<strong>Output:</strong> [1,3,5,2,4] |
| 15 | +</pre> |
| 16 | + |
| 17 | +<p><strong class="example">Example 2:</strong></p> |
| 18 | +<img alt="" src="https://assets.leetcode.com/uploads/2021/03/10/oddeven2-linked-list.jpg" style="width: 500px; height: 142px;" /> |
| 19 | +<pre> |
| 20 | +<strong>Input:</strong> head = [2,1,3,5,6,4,7] |
| 21 | +<strong>Output:</strong> [2,3,6,7,1,5,4] |
| 22 | +</pre> |
| 23 | + |
| 24 | +<p> </p> |
| 25 | +<p><strong>Constraints:</strong></p> |
| 26 | + |
| 27 | +<ul> |
| 28 | + <li>The number of nodes in the linked list is in the range <code>[0, 10<sup>4</sup>]</code>.</li> |
| 29 | + <li><code>-10<sup>6</sup> <= Node.val <= 10<sup>6</sup></code></li> |
| 30 | +</ul> |
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