Rotate List LeetCode Java

Posted 2020-11-14 昵称真难想

描述
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->nullptr and k = 2, return 4->5->1->2->3->nullptr.
分析
先遍历一遍，得出链表长度 len，注意 k 可能大于 len，因此令 k% = len。将尾节点 next 指针
指向首节点，形成一个环，接着往后跑 len ? k 步，从这里断开，就是要求的结果了。

代码

 1 public static ListNode rotateRight(ListNode head, int n) {
 2         if (head == null || head.next == null || n == 0)
 3             return head;
 4         ListNode fast = head, slow = head, countlen = head;
 5         ListNode newhead = new ListNode(-1);
 6         int len = 0;
 7 
 8         while (countlen != null) {
 9             len++;
10             countlen = countlen.next;
11         }
12 
13         n = n % len;
14         if (n == 0)
15             return head;
16         for (int i = 0; i < n; i++) {
17             fast = fast.next; // slow与fast间隔n+1
18         }
19         while (fast.next != null) {
20             slow = slow.next; // slow指向要倒着数的开始点的前一个位置。
21             fast = fast.next;
22 
23         }
24 
25         newhead = slow.next;
26         fast.next = head;
27         slow.next = null;
28 
29         return newhead;
30     }