public class KeypadSolution {
    public static void printKeypad(int input,String output) {
        if (input == 0) {
            System.out.println(output);
            return;
        }
        int rem = input % 10;
        char[] helperArray = helper(rem);
        printKeypad(input / 10, helperArray[0] + output);
        printKeypad(input / 10, helperArray[1] + output);
        printKeypad(input / 10, helperArray[2] + output);
        if (helperArray.length == 4) printKeypad(input / 10, helperArray[3] + output);
    }

    public static char[] helper(int n){
                 if (n == 2) return new char[]{'a', 'b', 'c'};
            else if (n == 3) return new char[]{'d', 'e', 'f'};
            else if (n == 4) return new char[]{'g', 'h', 'i'};
            else if (n == 5) return new char[]{'j', 'k', 'l'};
            else if (n == 6) return new char[]{'m', 'n', 'o'};
            else if (n == 7) return new char[]{'p', 'q', 'r', 's'};
            else if (n == 8) return new char[]{'t', 'u', 'v'};
            else if (n == 9) return new char[]{'w', 'x', 'y', 'z'};
            else             return new char[]{' '};
        }
    public static void main(String[] args){
        printKeypad(97,"");
        }
}