Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
Solution 1:
public boolean hasCycle(ListNode head) { ListNode walker = head, runner = head; do { if(runner == null || runner.next == null) return false; walker = walker.next; runner = runner.next.next; } while(walker != runner); return true; }
Solution 2:
public boolean hasCycle(ListNode head) { if(head == null) return false; ListNode walker = head, runner = head.next; while(runner != null) { if(walker == runner) return true; walker = walker.next; runner = runner.next; if(runner != null) runner = runner.next; } return false; }