{"id":641,"date":"2025-07-15T12:46:09","date_gmt":"2025-07-15T07:16:09","guid":{"rendered":"https:\/\/codeanddebug.in\/blog\/?p=641"},"modified":"2025-07-15T12:46:10","modified_gmt":"2025-07-15T07:16:10","slug":"linked-list-cycle-ii-leetcode-142","status":"publish","type":"post","link":"https:\/\/codeanddebug.in\/blog\/linked-list-cycle-ii-leetcode-142\/","title":{"rendered":"Linked List Cycle II | Leetcode 142 | Complete Guide with 2 Different Solutions"},"content":{"rendered":"\n

Given the head<\/code> of a linked list, return the node where the cycle begins. If there is no cycle, return <\/em>null<\/code>.<\/p>\n\n\n\n

Here’s the [Problem Link<\/span><\/mark><\/a><\/strong>] to begin with.<\/p>\n\n\n\n

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 next<\/code> pointer. Internally, pos<\/code> is used to denote the index of the node that tail’s next<\/code> pointer is connected to (0-indexed<\/strong>). It is -1<\/code> if there is no cycle. Note that<\/strong> pos<\/code> is not passed as a parameter<\/strong>.<\/p>\n\n\n\n

Do not modify<\/strong> the linked list.<\/p>\n\n\n\n

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

\"\"\/<\/figure>\n\n\n\n
Input:<\/strong> head = [3,2,0,-4], pos = 1
Output:<\/strong> tail connects to node index 1
Explanation:<\/strong> There is a cycle in the linked list, where tail connects to the second node.<\/pre>\n\n\n\n
Example 2:<\/strong><\/p>\n\n\n\n
\"\"\/<\/figure>\n\n\n\n
Input:<\/strong> head = [1,2], pos = 0
Output:<\/strong> tail connects to node index 0
Explanation:<\/strong> There is a cycle in the linked list, where tail connects to the first node.<\/pre>\n\n\n\n
Example 3:<\/strong><\/p>\n\n\n\n
\"\"\/<\/figure>\n\n\n\n
Input:<\/strong> head = [1], pos = -1
Output:<\/strong> no cycle
Explanation:<\/strong> There is no cycle in the linked list.<\/pre>\n\n\n\n
Constraints:<\/strong><\/p>\n\n\n\n