ListCycle.java


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import java.lang.*;
import java.util.*;
import node.*;

class ListCycle {
	public static boolean hasCycle(ListNode head) {
		if (head == null)
			return false;
		else if (head.next == null)
			return false;

		ListNode slow = head;
		ListNode fast = head.next;
		while (slow != null && fast.next != null) {
			if (slow == fast)
				return true;
			slow = slow.next;
			fast = fast.next.next;
		}
		return false;
	}

	public static void main(String[] args) {
		ListNode first = new ListNode(2, null);
		ListNode third = new ListNode(4, first);
		ListNode second = new ListNode(0, third);
		first.next = second;
		ListNode head = new ListNode(3, first);

		System.out.println(hasCycle(head));
	}
}