https://leetcode.com/problems/linked-list-cycle/
Approach 1: Hash Table1
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23/**
* 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;
Set<ListNode> nodeSeen=new HashSet<>();
while(!nodeSeen.contains(head)){
nodeSeen.add(head);
head=head.next;
if(head==null) return false;
}
return true;
}
}
Approach 2: Two Pointers1
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11public class Solution {
public boolean hasCycle(ListNode head) {
ListNode slow=head, fast=head;
while(fast!=null&&fast.next!=null){
slow=slow.next;
fast=fast.next.next;
if(slow==fast) return true;
}
return false;
}
}