61. Rotate List

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */

class Solution 
{
    static ListNode findNthNode(ListNode temp, int k)
    {
        int cnt = 1;
        while(temp != null)
        {
            if(cnt == k) 
            return temp ;
            
            cnt++;
            
            temp = temp.next ;
        }
            return temp;
    }


    public ListNode rotateRight(ListNode head, int k)
    {
        if(head == null || k == 0) 
        return head;
        
        ListNode tail = head;
        int len = 1;
        
        while(tail.next != null)
        {
            tail = tail.next;
            len += 1;
        }
            
            if(k % len == 0)
             return head;
             
            k = k % len;
             
            // attach the tail to the head
            tail.next = head;
             
            ListNode newLastNode = findNthNode(head, len -k);
            head = newLastNode.next;
            newLastNode.next = null ;
             
            return head;
    }
}