LeetCode 61. Rotate List

原题链接在这里：https://leetcode.com/problems/rotate-list/

题目：

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.

题解：

快慢指针, 先算长度len, runner停在tail node.

walker移动 len- k%len 步数后断开后面, runner.next指向head.

Note: corner case is k%len == 0. That is why we use dummy head.

Time Complexity: O(n). Space: O(1).

AC Java:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode rotateRight(ListNode head, int k) {
        if(head == null || head.next == null){
            return head;
        }
        
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode walker = dummy;
        ListNode runner = dummy;
        
        int len = 0;
        while(runner.next != null){
            runner = runner.next;
            len++;
        }
        
        int jump = len-(k%len);
        while(jump -- > 0){
            walker = walker.next;
        }
        
        runner.next = dummy.next;
        dummy.next = walker.next;
        walker.next = null;
        
        return dummy.next;
    }
}

与Rotate Array相似