Linked List Cycle

EasyLinked ListsTwo Pointers

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given head, the head of a linked list, determine if the linked list has a cycle in it. 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 pointer. Return true if there is a cycle in the linked list, otherwise return false.

Examples

Input: head = [3,2,0,-4], pos = 1
Output: true
There is a cycle: tail connects to node at index 1.
Input: head = [1,2], pos = 0
Output: true
Input: head = [1], pos = -1
Output: false

Constraints

  • The number of nodes in the list is in the range [0, 10^4].
  • -10^5 <= Node.val <= 10^5
  • pos is -1 or a valid index in the linked list.

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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