Rotate List, from LeetCode

rotate_list.cpp

/**
 * In an interview, the following questions should be asked:
 *  (1) What happens if k is longer than the list size
 *  (2) Edge cases (if head is NULL and k may be zero)
 * 
 *  Analysis: (where n is the number of nodes in the list)
 *   Time: O(n)
 *   Space: O(1)
 */

class Solution {
public:
    ListNode *rotateRight(ListNode *head, int k) {
        ListNode *tail=head,
                 *kBehindTail=head;
        
        if (!k || !head) return head;
        
        for (int i=0; i < k; i++) {
            tail=tail->next;
            if (!tail) tail = head; //K longet than list size, so restart it again
        }
        
        while (tail->next) {
            tail=tail->next;
            kBehindTail=kBehindTail->next;
        }
        
        tail->next = head;
        head = kBehindTail->next;
        kBehindTail->next = NULL;
        
        return head;
    }
};