Given a list, rotate the list to the right by k places, where k is non-negative.

For example:
Given1->2->3->4->5->NULLand k =2,
return4->5->1->2->3->NULL.

/**
 * 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==nullptr||k==0)
            return head;
        int len=1;
        ListNode *p=head;
        while(p->next){
            //遍歷一遍，求出鏈表長度
            len++;
            p=p->next;
        }
        k=len-k%len;
         
        p->next=head;//首尾相連
        for(int step=0;step<k;step++){
            p
 
=p->next;//接著往後跑
        }
        head=p->next;//新的首節點
        p->next=nullptr;//斷開環
        return head;
    }
};

rotate-list 旋轉部分鏈表