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Linked List Cycle | CodeTutor

Linked List Cycle

Easy

Hash Tables Linked Lists Two Pointers Fast & Slow Pointers

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. Internally, pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter.

Return true if there is a cycle in the linked list. Otherwise, return false.

Constraints

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

Examples

Input: head = [3,2,0,-4], pos = 1

Output: true

There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).

Input: head = [1,2], pos = 0

Output: true

There is a cycle in the linked list, where the tail connects to the 0th node.

Input: head = [1], pos = -1

Output: false

There is no cycle in the linked list.

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