Rotate List LeetCode Java

描述
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->nullptr and k = 2, return 4->5->1->2->3->nullptr.
分析
先遍历一遍，得出链表长度 len，注意 k 可能大于 len，因此令 k% = len。将尾节点 next 指针
指向首节点，形成一个环，接着往后跑 len − k 步，从这里断开，就是要求的结果了。

代码

public static ListNode rotateRight(ListNode head, int n) {
        if (head == null || head.next == null || n == 0)
            return head;
        ListNode fast = head, slow = head, countlen = head;
        ListNode newhead = new ListNode(-1);
        int len = 0;

        while (countlen != null) {
            len++;
            countlen = countlen.next;
        }

        n = n % len;
        if (n == 0)
            return head;
        for (int i = 0; i < n; i++) {
            fast = fast.next; // slow与fast间隔n+1
        }
        while (fast.next != null) {
            slow = slow.next; // slow指向要倒着数的开始点的前一个位置。
            fast = fast.next;

        }

        newhead = slow.next;
        fast.next = head;
        slow.next = null;

        return newhead;
    }