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.

先把链串起来，连成环。然后将head往后移动(len-k%len)次，再把链断开。整个思路也非常清晰。

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *rotateRight(ListNode *head, int k) {
12         if (head == NULL) return head;
13         int len = 1;
14         ListNode *tail = head, *prev;
15         while (tail->next) {
16             len++;
17             tail = tail->next;
18         }
19         tail->next = head;
20         k = len - (k % len);
21         for (int i = 0; i < k; i++) {
22             prev = head;
23             head = head->next;
24         }
25         prev->next = NULL;
26         return head;
27     }
28 };