LeetCode - Linked List Cycle II

Linked List Cycle II

//
public ListNode detectCycle(ListNode head) {
        if(head == null || head.next == null || head.next.next == null) return null;
        ListNode runner = head;
        ListNode walker = head;
        while(runner.next != null && runner.next.next != null){
            runner = runner.next.next;
            walker = walker.next;
            if(runner == walker) break;
        }
        while(head != null && walker != null && head != walker){
            head = head.next;
            walker = walker.next;
        }
        return walker;
    }
    
//
public ListNode detectCycle(ListNode head) {
        if(head==null) return head;
        ListNode walker = head;
        ListNode runner = head;
        while(runner.next!=null && runner.next.next!=null){
            walker = walker.next;
            runner = runner.next.next;
            if(walker == runner)
                break;
        }
        if(runner.next==null || runner.next.next==null) return null;
        ListNode cur = head;
        while(cur!=runner){
            cur = cur.next;
            runner = runner.next;
        }
        return cur;
    }