Linked List Cycle

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

 

/**
 * 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 || head.next.next == null) {
        	return false;
        }
        ListNode n1 = head.next;
        ListNode n2 = head.next.next;
        while (n1 != n2) {
        	if (n2.next == null || n2.next.next == null) {
        		return false;
        	}
        	n1 = n1.next;
        	n2 = n2.next.next;
        }
        return true;
    }
}