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51 lines
2.4 KiB
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51 lines
2.4 KiB
HTML
<p>In a linked list of size <code>n</code>, where <code>n</code> is <strong>even</strong>, the <code>i<sup>th</sup></code> node (<strong>0-indexed</strong>) of the linked list is known as the <strong>twin</strong> of the <code>(n-1-i)<sup>th</sup></code> node, if <code>0 <= i <= (n / 2) - 1</code>.</p>
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<ul>
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<li>For example, if <code>n = 4</code>, then node <code>0</code> is the twin of node <code>3</code>, and node <code>1</code> is the twin of node <code>2</code>. These are the only nodes with twins for <code>n = 4</code>.</li>
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</ul>
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<p>The <strong>twin sum </strong>is defined as the sum of a node and its twin.</p>
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<p>Given the <code>head</code> of a linked list with even length, return <em>the <strong>maximum twin sum</strong> of the 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/2021/12/03/eg1drawio.png" style="width: 250px; height: 70px;" />
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<pre>
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<strong>Input:</strong> head = [5,4,2,1]
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<strong>Output:</strong> 6
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<strong>Explanation:</strong>
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Nodes 0 and 1 are the twins of nodes 3 and 2, respectively. All have twin sum = 6.
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There are no other nodes with twins in the linked list.
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Thus, the maximum twin sum of the linked list is 6.
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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/2021/12/03/eg2drawio.png" style="width: 250px; height: 70px;" />
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<pre>
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<strong>Input:</strong> head = [4,2,2,3]
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<strong>Output:</strong> 7
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<strong>Explanation:</strong>
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The nodes with twins present in this linked list are:
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- Node 0 is the twin of node 3 having a twin sum of 4 + 3 = 7.
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- Node 1 is the twin of node 2 having a twin sum of 2 + 2 = 4.
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Thus, the maximum twin sum of the linked list is max(7, 4) = 7.
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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/2021/12/03/eg3drawio.png" style="width: 200px; height: 88px;" />
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<pre>
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<strong>Input:</strong> head = [1,100000]
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<strong>Output:</strong> 100001
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<strong>Explanation:</strong>
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There is only one node with a twin in the linked list having twin sum of 1 + 100000 = 100001.
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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 an <strong>even</strong> integer in the range <code>[2, 10<sup>5</sup>]</code>.</li>
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<li><code>1 <= Node.val <= 10<sup>5</sup></code></li>
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</ul>
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