旋转链表

/**
 * 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 || k == 0){
            return head;
        }
        
        ListNode *p = head;
        ListNode *tail = NULL;
        int len = 1;
        while(p->next != 0){
            len++;
            p = p->next;
        }
        tail = p;
        if(len == k){
            return head;
        }
        else if(len < k){
            int m = k%len;
            if(m == 0){
                return head;
            }
            else{
                return move(head, tail, len-m);
            }
        }
        else{
            return move(head, tail, len-k);
        }
    }
    
    ListNode* move(ListNode* head, ListNode* tail, int k){
        ListNode *p = head;
        for(int i = 1; i < k; i++){
            p = p->next;
        }
        tail->next = head;
        head = p->next;
        p->next = NULL;
        return head;
    }
};