141. Linked List Cycle

141. Linked List Cycle

Given a linked list, determine if it has a cycle in it.

Follow up: Can you solve it without using extra space?

/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * } * } */public class Solution { public boolean hasCycle(ListNode head) { if(head==null){ return false; } ListNode fast=head; ListNode low=head; while(fast!=null&&fast.next!=null){ fast=fast.next.next; low=low.next; if(fast==low){ return true; } } return false; }}

/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * } * } */public class Solution { public boolean hasCycle(ListNode head) { if (head == null || head.next == null) return false; if (head.next == head) return true; ListNode next = head.next; head.next = head; return hasCycle(next); }}

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