https://leetcode.com/problems/rotate-list/

LinkedListRotate.java

package dsa;

public class LinkedListRotate {
	
	public static void main(String[] args) 
	{
		ListNode n1 = new ListNode(1); ListNode n2 = new ListNode(2); ListNode n3 = new ListNode(3); ListNode n4 = new ListNode(4); ListNode n5 = new ListNode(5);
		n1.next = n2; n2.next = n3; n3.next = n4; n4.next = n5;
		
		System.out.println(getLength(n1));
		print(n1);
		
		ListNode head = rotateRight(n1, 1);
		print(head);
	}
	
	public static ListNode rotateRight(ListNode head, int k) {
		int len = getLength(head);
		
		if (len <= 1 || k == 0 || len == k) {
		    return head;
		}
		
		int r = k % len;
		if( r == 0) {
		    return head;
		}
		
		// New head's location is (len - r).
		// Get the location of newHead and it's predecessor.
		ListNode newHeadsPredecessor = head;
		for(int i=1;i< len-r;i++) {
			newHeadsPredecessor = newHeadsPredecessor.next;
		}
		
		ListNode newHead = newHeadsPredecessor.next;
		// Set newHead's predecessor as the new endnode.
		newHeadsPredecessor.next = null;
		
		// Go to the current endNode.
		ListNode endNode = newHead;
		while(endNode.next != null) {
			endNode = endNode.next;
		}
		// connect it to current head node
		endNode.next = head;
		
		// elevate the new-head as head node.
		return newHead;
	}
	
	private static void print(ListNode head) {
		while(head != null) {
			System.out.print(head.val + "->");
			head = head.next;
		}		
		System.out.println();
	}

	private static int getLength(ListNode head) {
		int len = 0;
		while(head != null) {
			head = head.next;
			len++;
		}
		
		return len;
	}
}

class ListNode {
      int val;
      ListNode next;
      ListNode(int x) { val = x; }
  }