public class MidtermReview {
    public static void main(String[] args) {
        System.out.println(undouble("bookkeeper"));
    }

    public static String undouble(String s) {
        if (s.length() < 2) {
            return s;
        } else {
            char c1 = s.charAt(0);
            char c2 = s.charAt(1);
            if (c1 == c2) {
                return c1 + undouble(s.substring(2));
            } else {
                return c1 + undouble(s.substring(1));
            }
        }
    }

    /* Bugg Version
    public String undouble(String s) {
        if (s.isEmpty()) { // Bug: Wrong base case
            return s;
        } else {
            char c1 = s.charAt(0);
            char c2 = s.charAt(1);
            if (c1 == c2) {
                return c1 + undouble(s.substring(2));
            } else {
                // Bug: Doesn't work for "books"
                return c1 + (c2 + undouble(s.substring(2)));
            }
        }
    }
    */
}