【leetcode】61. 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) {
        if(head==NULL||head->next==NULL||k==0)
            return head;
        ListNode* bf=head;
        ListNode* newhead=head,*end=head;
        int length=1;
        while(end->next!=NULL){
            end=end->next;
            length++;
        }
        end=head;
        if(k>length){
            k=k%length;
        }
        if(k==length||k==0)
            return head;
        k--;
        while(k>0&&end->next!=NULL){
            end=end->next;
            k--;
        }
        while(end->next!=NULL){
            end=end->next;
            bf=newhead;
            newhead=newhead->next;
        }

        bf->next=NULL;
        end->next=head;
        return newhead;

    }
};