Telephone Words

import java.util.ArrayList;
import java.util.HashMap;

/*
 * Write a program that takes a telephone number as input and print out all the possible "words"
 * or combinations of letters that can represent the given number.
 *
 * Input:Digit string “23"
 * Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
 * Note:
 * Although the above answer is in lexicographical order, your answer could be in any order you want.
 */

public class PhoneNumber {

    public static void main(String[] args) {
        for (String sb : letterCombinations("1203")) {
            System.out.println(sb);
        }
    }


    public static ArrayList<String> letterCombinations(String digits) {
        ArrayList<String> result = new ArrayList<String>();
        getLetters(digits, 0, new String(), result, getMap());
        return result;

    }


    private static void getLetters(String digits, int index, String sofar,
                    ArrayList<String> result, HashMap<Character, String> map) {

        if (index == digits.length()) {
            result.add(sofar);
        }
        else if (digits.charAt(index) == '1') {
            getLetters(digits, index+1, sofar, result, map);
        }
        else {
            String letters = map.get(digits.charAt(index));
            for (int i = 0; i < letters.length(); i++) {
                getLetters(digits, index+1, sofar + letters.charAt(i), result, map);
            }
        }
    }


    private static HashMap<Character, String> getMap() {
        HashMap<Character, String> map = new HashMap<Character, String>();
        map.put('1', "");
        map.put('2', "abc");
        map.put('3', "def");
        map.put('4', "ghi");
        map.put('5', "jkl");
        map.put('6', "mno");
        map.put('7', "pqrs");
        map.put('8', "tuv");
        map.put('9', "wxyz");
        map.put('0', " ");
        return map;
    }
}