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;
}
}