旋转链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    /**
     * @param head: the List
     * @param k: rotate to the right k places
     * @return: the list after rotation
     */
    public ListNode rotateRight(ListNode head, int k) {
        if (head == null || head.next == null) {
            return head;
        }
        
        //获取链表长度，并得到尾节点的指针。
        int len = 1;
        ListNode p = head;
        while (p.next != null) {
            p = p.next;
            len++;
        }
        
        k = k % len;  //去除需要多旋转的圈数
        p.next = head; //将链表首尾相连，结成环形。
        for (int i = 0; i < len - k; i++) {
            p = p.next;     //旋转链表
        }
        head = p.next;  //新的链表头
        p.next = null;  //断开环形链表。
        return head;
    }
}