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

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

O(n) time O(1) space

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/**
 * 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;
        ListNode slower = head, faster = head;
        
        while (faster != null && faster.next != null){
            slower = slower.next;
            faster = faster.next.next;
            if (slower == faster){
                return true;
            }
        }
        
        return false;
    }
}