LinkedListCycle.java

/**
 * Given a linked list, determine if it has a cycle in it.
 *
 * <p>Follow up: Can you solve it without using extra space?
 */
public class LinkedListCycle {
 public boolean hasCycle(ListNode head) {
 if (head == null) return false;
 ListNode fast = head;
 ListNode late = head;
 do {
 fast = fast.next;
 late = late.next;
 if (late == null) {
 return false;
 } else {
 late = late.next;
 if (fast == late) {
 return true;
 }
 }
 } while (fast != null && late != null);
 return false;
 }
}