Rotate List LeetCode

Recursion is very simple.

 public ListNode rotateRight(ListNode head, int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
     
       if (head==null || head.next == null) return head;
       if (n==0) return head;
     
       ListNode curr = head;
       ListNode prev = head;
     
       while (curr.next != null) {
           prev = curr;
           curr = curr.next;
       }
     
       curr.next = head;
       prev.next = null;
     
       return rotateRight(curr, n-1);
    }

1. n may be larger than the length of list.
2. Non-recursion

public ListNode rotateRight(ListNode head, int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
       if (head==null || head.next ==null) return head;
       ListNode dummy = new ListNode(0);
       dummy.next = head;
       int len = listLen(head);
       n%=len;
       ListNode p = dummy, q = dummy;
       int i=0;
       while (q.next != null) {
           if (i>=n) {
               p=p.next;
           }
           q=q.next;
           i++;
       }
       q.next = dummy.next;
       dummy.next = p.next;
       p.next = null;
       return dummy.next;
    }
   
    private int listLen(ListNode p) {
        int len = 0;
        while (p != null) {
            len++;
            p = p.next;
        }
        return len;
    }