[LeetCode] Grind 75 questions (12/75) Linked List Cycle

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28

/**
 * 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 slow = head;
        ListNode fast = head.next;

        while(slow != fast) {
            if(fast == null || fast.next == null) return false;

            slow = slow.next;
            fast = fast.next.next;
        }

        return true;
    }
}