lintcode 170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:
    /**
     * @param head: the list
     * @param k: rotate to the right k places
     * @return: the list after rotation
     */
    ListNode *rotateRight(ListNode *head, int k) {
        // write your code here
        if(head==NULL)
        return NULL;
        int len=1;
        ListNode* p1=head;
        while(p1->next!=NULL)
        {
            len++;
            p1=p1->next;
        }
        
        k=k%len;
        if(k==0)
        return head;
        
        int step1=len-k-1;
        p1=head;
        while(step1--)
        p1=p1->next;
        
        ListNode* p2=p1->next;
        ListNode* p3=p2;
        while(p3->next!=NULL)
        p3=p3->next;
        
        p3->next=head;
        p1->next=NULL;
        return p2;
    }
};