leetcode61 Rotate List

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.

/**
 * 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) {
        ListNode *ans=NULL;
        
        int size=0;
        ListNode *p=head;
        while(p)
        {
            size++;
            p=p->next;
        }
        if(size==0)
            return ans;
        
        k=k%size;
        
        if(k==0)
            return head;
        
        int t=size-k;
        p=head;
        while(--t)
        {
            p=p->next;
        }
        ListNode*pp=p->next;
        p->next=NULL;
        ans=pp;
        while(pp->next!=NULL)
        {
            pp=pp->next;
        }
        pp->next=head;
        return ans;
        
    }
    
};