class ListNode {

int val;

ListNode next;

ListNode(int x) {

val = x;

next = null;

}

}

public class Solution {

public boolean hasCycle(ListNode head) {

// IMPORTANT: Please reset any member data you declared, as

// the same Solution instance will be reused for each test case.

ListNode fast = head;

ListNode slow = head;

while (fast != null) {

slow = slow.next;

fast = fast.next;

if (fast == null || fast.next == null) { // fast reaches to the end of

// list

return false;

}

fast = fast.next;

if (fast == slow) { // fast meets slow

return true;

}

}

return false;

}

}