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 || head->next == NULL)
            return head;
        
        ListNode* tail = head;
        int n = 1;
        while (tail->next) {
            n++;
            tail = tail->next;
        }
        
        if (k >= n)
            k = k % n;
        
        if (k == 0)
            return head;
        
        int time = n - k - 1;
        ListNode* pre = head;

        while(time--) {
            pre = pre->next;
        }
        
        ListNode* head2 = pre->next;
        
        tail->next = head;
        pre->next = NULL;
        return head2;
    }
};