LeetCode Rotate List

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->NULL and k = 2,
return 4->5->1->2->3->NULL.

按照倒数第K位进行旋转

定义两个指针来表示链表最后K位

K可能大于list的长度，则从head开始继续移动，直到n=0

注意链表结尾赋为null

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int n) {
        if (head == null)
			return head;
		if (n == 0)
			return head;
		ListNode p1 = null;
		ListNode p2 = null;
		int num = n;
		while (num > 0) {
			p1 = head;
			num--;
			while (num > 0 && p1.next != null) {
				p1 = p1.next;
				num--;
			}
		}
		if (num == 0) {   //p2与p1相距k个位置
			while (p1.next != null) {
				p1 = p1.next;
				if(p2==null)
					p2=head;
				else p2 = p2.next;
			}
		}
		if(p2!=null){
			p1.next = head;  //旋转
			head=p2.next;
			p2.next=null;   //注意链表结尾要赋为null
		}
		return head;
    }
}