[leetcode]61. Rotate List反转链表k个节点

public ListNode rotateRight(ListNode head, int k) {
        //特殊情况
        if (head==null||head.next==null||k==0) return head;
        int len = 0;
        ListNode p = head;
        //计算链表长度，防止k大于长度
        while (p!=null)
        {
            len++;
            p = p.next;
        }
        //k大于等于len的情况
        k = k>=len?k%len:k;
        if (k==0) return head;
        //下边是链表取后k个节点的方法，重要，双指针
        p = head;
        while (k-->0)
        {
            p = p.next;
        }
        ListNode q = head;
        while (p.next!=null)
        {
            p = p.next;
            q = q.next;
        }
        //找到目标节点开始位置
        ListNode res = q.next;
        //将原链表断开位置的后边置为null
        q.next=null;
        //将前边的链表接上
        ListNode temp = res;
        while (temp.next!=null)
        {
            temp = temp.next;
        }
        temp.next = head;
        return res;
    }