LeetCode 61. Rotate List

/**
 * 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;
        if(k==0)
            return head;
        ListNode* end ;
        ListNode* start = head;
        ListNode* pre;
        ListNode* term =head;
        
        int len=1;
        
        while(head->next!=NULL)
        {
            head = head->next;
            len++;
        }
        
        if(len==1)
            return head;
        
        end = head;
        
        int n = k%len;
        
        if(n==0)
            return start;
        
        int m = len-n;
        
        head = start;
        int i=0;
        while(head!=NULL)
        {
            if(i==m)
            {
                start = head;
                break;
            }
            if(i==m-1)
            {
                pre=head;
            }
            
            i++;
            
            head=head->next;
        }
        
        pre->next=NULL;
        end->next=term;
        
       
        
        return start;
    }
};