旋转链表

题目链接：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){
            return NULL;
        }
        int len = 0;
        ListNode* p = head;
        //首先计算出来整个链表的长度
        while(p){
            len++;
            p = p->next;
        }
        
        k = k%len;
        k = len - k;
        //取模运算，调整数据
        //边界情况判断
        if(k == 0 || k == len){
            return head;
        }
        int i;
        //找到应当断开的地方
        for(i = 0,p = head;p!=NULL&&i<k-1;i++,p=p->next);
        //cout << " p = " << p->val << endl;
        ListNode* q = p->next;  //记录新的首元结点
        p->next = NULL;         //断开操作
        p = q;
        while(p->next){
            p = p->next;
        }
        p->next = head;
        head = q;
        return q;
    }
};