leetcode-problemset/leetcode-cn/problem (English)/环路检测(English) [linked-list-cycle-lcci].html

<p>Given a circular linked list, implement an algorithm that returns the node at the beginning of the loop.</p>

<p>Circular linked list: A (corrupt) linked list in which a node&#39;s next pointer points to an earlier node, so as to make a loop in the linked list.</p>

<p><strong>Example 1: </strong></p>

<pre>
<strong>Input: </strong>head = [3,2,0,-4], pos = 1
<strong>Output: </strong>tail connects to node index 1</pre>

<p><strong>Example 2: </strong></p>

<pre>
<strong>Input: </strong>head = [1,2], pos = 0
<strong>Output: </strong>tail connects to node index 0</pre>

<p><strong>Example 3: </strong></p>

<pre>
<strong>Input: </strong>head = [1], pos = -1
<strong>Output: </strong>no cycle</pre>

<p><strong>Follow Up: </strong><br />
Can you solve it without using additional space?</p>