leetcode-problemset/算法题/linked-list-cycle.json

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            "title": "Linked List Cycle",
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            "content": "<p>Given <code>head</code>, the head of a linked list, determine if the linked list has a cycle in it.</p>\n\n<p>There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the&nbsp;<code>next</code>&nbsp;pointer. Internally, <code>pos</code>&nbsp;is used to denote the index of the node that&nbsp;tail&#39;s&nbsp;<code>next</code>&nbsp;pointer is connected to.&nbsp;<strong>Note that&nbsp;<code>pos</code>&nbsp;is not passed as a parameter</strong>.</p>\n\n<p>Return&nbsp;<code>true</code><em> if there is a cycle in the linked list</em>. Otherwise, return <code>false</code>.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist.png\" style=\"width: 300px; height: 97px; margin-top: 8px; margin-bottom: 8px;\" />\n<pre>\n<strong>Input:</strong> head = [3,2,0,-4], pos = 1\n<strong>Output:</strong> true\n<strong>Explanation:</strong> There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).\n</pre>\n\n<p><strong>Example 2:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist_test2.png\" style=\"width: 141px; height: 74px;\" />\n<pre>\n<strong>Input:</strong> head = [1,2], pos = 0\n<strong>Output:</strong> true\n<strong>Explanation:</strong> There is a cycle in the linked list, where the tail connects to the 0th node.\n</pre>\n\n<p><strong>Example 3:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2018/12/07/circularlinkedlist_test3.png\" style=\"width: 45px; height: 45px;\" />\n<pre>\n<strong>Input:</strong> head = [1], pos = -1\n<strong>Output:</strong> false\n<strong>Explanation:</strong> There is no cycle in the linked list.\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li>The number of the nodes in the list is in the range <code>[0, 10<sup>4</sup>]</code>.</li>\n\t<li><code>-10<sup>5</sup> &lt;= Node.val &lt;= 10<sup>5</sup></code></li>\n\t<li><code>pos</code> is <code>-1</code> or a <strong>valid index</strong> in the linked-list.</li>\n</ul>\n\n<p>&nbsp;</p>\n<p><strong>Follow up:</strong> Can you solve it using <code>O(1)</code> (i.e. constant) memory?</p>\n",
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