61. 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.

题目含义：从列表的末尾依次翻转k个元素到头部

    public ListNode rotateRight(ListNode head, int k) {
        if (head==null||head.next==null) return head;
        ListNode dummy=new ListNode(0);
        dummy.next=head;
        ListNode fast=dummy,slow=dummy;
        int length=0;
        while (fast.next!=null)
        {
            length++;
            fast = fast.next;
        }
        for (int j=length-k%length;j>0;j--) //Get the i-n%i th node
            slow=slow.next;
        fast.next=dummy.next; //Do the rotation
        dummy.next=slow.next;
        slow.next=null;
        return dummy.next;     
    }