Rotate List

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

For example:
Given 1->2->3->4->5->NULL and k = 2,
return 4->5->1->2->3->NULL.

public ListNode rotateRight(ListNode head, int k) {

    if (head == null || head.next == null) return head;

    ListNode fast = head, slow = head, dummyHead = head;
    int len = 0;

    while (fast.next != null){
        fast = fast.next;
        if (++len > k)
            slow = slow.next;
    }

    len ++;

    if(k >= len){
        k %= len;
        int offset = len - k;
        while (-- offset > 0)
            slow = slow.next;
    }

    //if(k == 0) return head;
    if(slow.next != null){
        dummyHead = slow.next;
        slow.next = null;
        fast.next = head;       
    }

    return dummyHead;
}