[Java] Prompt the user for a phone number. Output all the possible phone numbers that use the letters on the keyboard. For example, the phone number 123-4567 will have as one of its combinations 1CFILOQ. Do not use loops. Use recursion.

Standard Input

0

1

2

3

4

5

6

7

8

9

Standard Output

0

1

A B C

D E F

G H I

J K L

M N O

P Q R S

T U V

W X Y Z