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。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *rotateRight(ListNode *head, int k) {
        if (head == NULL) return head;
        int len = 1;
        ListNode *tail = head, *prev;
        while (tail->next) {
            len++;
            tail = tail->next;
        }
        tail->next = head;
        k = len - (k % len);
        for (int i = 0; i < k; i++) {
            prev = head;
            head = head->next;
        }
        prev->next = NULL;
        return head;
    }
};