Rotate List

Given a linked list, rotate the list to the right by k places, where k is non-negative.

Example 1:

Input: 1->2->3->4->5->NULL, k = 2
Output: 4->5->1->2->3->NULL
Explanation:
rotate 1 steps to the right: 5->1->2->3->4->NULL
rotate 2 steps to the right: 4->5->1->2->3->NULL

Example 2:

Input: 0->1->2->NULL, k = 4
Output: 2->0->1->NULL
Explanation:
rotate 1 steps to the right: 2->0->1->NULL
rotate 2 steps to the right: 1->2->0->NULL
rotate 3 steps to the right: 0->1->2->NULL
rotate 4 steps to the right: 2->0->1->NULL

class Solution {
    public int len(ListNode node) {
        int len = 0;
        while (node != null) {
            len++;
            node = node.next;
        }
        return len;
    }

    public ListNode rotateRight(ListNode head, int k) {
        if (head == null)
            return head;
        int len = len(head);
        k = k % len;
        if (k == 0)
            return head;
        int headIndex = len - k, index = 0;
        ListNode temp = head;
        ListNode ans = null;
        while (temp.next != null) {
            if (index + 1 == headIndex) {
                ans = temp.next;
                temp.next = null;
                temp = ans;
            } else
                temp = temp.next;
            index++;
        }
        temp.next = head;
        return ans;
    }
}