61.旋转链表

给你一个链表的头节点 head，旋转链表，将链表每个节点向右移动 k 个位置。

 

示例 1：


输入：head = [1,2,3,4,5], k = 2
输出：[4,5,1,2,3]
示例 2：


输入：head = [0,1,2], k = 4
输出：[2,0,1]
 

提示：

链表中节点的数目在范围 [0, 500] 内
-100 <= Node.val <= 100
0 <= k <= 2 * 109

func rotateRight(head *ListNode, k int) *ListNode {
	if head == nil || head.Next == nil || k == 0 {
		return head
	}
	dummyHead := &ListNode{Next: head}

	tail := dummyHead.Next
	n := 1 //这里为啥是 1？因为包括了头节点
	for tail.Next != nil {
		n++
		tail = tail.Next
	}
	if k%n == 0 {
		return head
	}

	kNode := dummyHead
	for step := n - k%n; step > 0; step-- {
		kNode = kNode.Next
	}
	tail.Next = head
	dummyHead.Next = kNode.Next
	kNode.Next = nil
	return dummyHead.Next
}