LeetCode | Rotate List

题目：

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

.

思路：

首先计算出链表元素个数，然后利用k mod 元素个数，求出实际需要的右移动次数。最后通过快慢指针来实现右移。

代码：

/**
 * 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;
        }
        if(k<=0)
        {
            return head;
        }
        
        ListNode*p=head;
        int count=0;
        while(p!=NULL)
        {
            p=p->next;
            count++;
        }
        k=k%count;
        
        ListNode*slow=head;
        ListNode*fast=head;
        
        for(int i=0;i<k;i++)
        {
            if(fast->next==NULL)
            {
                break;
            }
            fast=fast->next;
        }
        while(fast->next!=NULL)
        {
            slow=slow->next;
            fast=fast->next;
        }
        fast->next=head;
        head=slow->next;
        slow->next=NULL;
        return head;
    }
};