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.

Anaylisis: Linked List题目的做法其实比较固定，就是Runner Technique(Two pointer) 方法加上 Dummy Node(设置一个head之前的虚假节点)两种方法，这道题就这样搞一搞就出来了。

需要注意的是：处理null 输入需要特别考虑，然后，需要找到新的linked list的头

第二遍做法：注意15行需要特别处理，wrap up了之后n=0的情况

public class Solution {
    public ListNode rotateRight(ListNode head, int n) {
        if (head == null) return null;
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode cursor = dummy;
        ListNode walker = dummy;
        ListNode runner = dummy;
        int count = 0;
        while (cursor.next != null) {
            cursor = cursor.next;
            count ++;
        }
        n %= count;
        if (n == 0) return head;
        while (n > 0) {
            runner = runner.next;
            n--;
        }
        while (runner.next != null) {
            runner = runner.next;
            walker = walker.next;
        }
        dummy.next = walker.next;
        walker.next = runner.next;
        runner.next = head;
        return dummy.next;
    }
}