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57 lines
2.8 KiB
HTML
57 lines
2.8 KiB
HTML
<p>You are given the <code>head</code> of a linked list.</p>
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<p>The nodes in the linked list are <strong>sequentially</strong> assigned to <strong>non-empty</strong> groups whose lengths form the sequence of the natural numbers (<code>1, 2, 3, 4, ...</code>). The <strong>length</strong> of a group is the number of nodes assigned to it. In other words,</p>
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<ul>
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<li>The <code>1<sup>st</sup></code> node is assigned to the first group.</li>
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<li>The <code>2<sup>nd</sup></code> and the <code>3<sup>rd</sup></code> nodes are assigned to the second group.</li>
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<li>The <code>4<sup>th</sup></code>, <code>5<sup>th</sup></code>, and <code>6<sup>th</sup></code> nodes are assigned to the third group, and so on.</li>
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</ul>
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<p>Note that the length of the last group may be less than or equal to <code>1 + the length of the second to last group</code>.</p>
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<p><strong>Reverse</strong> the nodes in each group with an <strong>even</strong> length, and return <em>the</em> <code>head</code> <em>of the modified linked list</em>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/10/25/eg1.png" style="width: 699px; height: 124px;" />
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<pre>
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<strong>Input:</strong> head = [5,2,6,3,9,1,7,3,8,4]
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<strong>Output:</strong> [5,6,2,3,9,1,4,8,3,7]
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<strong>Explanation:</strong>
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- The length of the first group is 1, which is odd, hence no reversal occurs.
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- The length of the second group is 2, which is even, hence the nodes are reversed.
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- The length of the third group is 3, which is odd, hence no reversal occurs.
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- The length of the last group is 4, which is even, hence the nodes are reversed.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/10/25/eg2.png" style="width: 284px; height: 114px;" />
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<pre>
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<strong>Input:</strong> head = [1,1,0,6]
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<strong>Output:</strong> [1,0,1,6]
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<strong>Explanation:</strong>
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- The length of the first group is 1. No reversal occurs.
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- The length of the second group is 2. The nodes are reversed.
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- The length of the last group is 1. No reversal occurs.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/11/17/ex3.png" style="width: 348px; height: 114px;" />
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<pre>
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<strong>Input:</strong> head = [1,1,0,6,5]
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<strong>Output:</strong> [1,0,1,5,6]
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<strong>Explanation:</strong>
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- The length of the first group is 1. No reversal occurs.
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- The length of the second group is 2. The nodes are reversed.
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- The length of the last group is 2. The nodes are reversed.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li>The number of nodes in the list is in the range <code>[1, 10<sup>5</sup>]</code>.</li>
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<li><code>0 <= Node.val <= 10<sup>5</sup></code></li>
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</ul>
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