/**
knakul853
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) { // reverse n-k and k then reverse whole list.

        if( !head ) return NULL;
        int len = 0;
        ListNode* root = head;

        while( root ){
            root = root->next;
            len++;
        }

        k = k % len;

          k = len - k;
        ListNode* a = head;

        int tem = k;

        while(k--){
            a = a->next;
        }

        auto first = reverseByK(head, tem);
        ListNode* ans = first;
        auto second = reverseByK(a);
        while(first->next)
        {
            first = first->next;
        }

        first->next = second;

       return reverseByK(ans);

    }

    ListNode* reverseByK(ListNode* root, int k=INT_MAX )
    {
        if(!root) return NULL;

        ListNode* pre = NULL;

        while( k && root )
        {
           ListNode* save =  root->next;
            root->next= pre;
            pre = root;
            root = save;
            k--;
        }

        return pre;
    }
};