61. 旋转链表

输入: 1->2->3->4->5->NULL, k = 2
输出: 4->5->1->2->3->NULL
解释:
向右旋转 1 步: 5->1->2->3->4->NULL
向右旋转 2 步: 4->5->1->2->3->NULL

输入: 0->1->2->NULL, k = 4
输出: 2->0->1->NULL
解释:
向右旋转 1 步: 2->0->1->NULL
向右旋转 2 步: 1->2->0->NULL
向右旋转 3 步: 0->1->2->NULL
向右旋转 4 步: 2->0->1->NULL

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null || head.next == null || k <= 0) {
            return head;
        }
        int length = len(head);
        int realK = k % length;
        //移动0个位置
        if (0 == realK) {
            return head;
        }
        ListNode fast = head;
        ListNode slow = head;
        for (int i = 0; i < realK; i++) {
            fast = fast.next;
        }
        while (fast.next != null) {
            fast = fast.next;
            slow = slow.next;
        }
        ListNode tmp = slow;
        slow = slow.next;
        tmp.next = null;
        fast.next = head;
        return slow;
    }

    private int len(ListNode head) {
        int count = 0;
        while (head != null) {
            count++;
            head = head.next;
        }
        return count;
    }
}