How can I print out all possible letter combinations a given phone number can represent?

Question

I just tried for my first programming interview and one of the questions was to write a program that given a 7 digit telephone number, could print all possible combinations

Answer 1

Here is the working code for the same.. its a recursion on each step checking possibility of each combinations on occurrence of same digit in a series....I am not sure if there is any better solution then this from complexity point of view.....

Please let me know for any issues....

import java.util.ArrayList;


public class phonenumbers {

    /**
     * @param args
     */
    public static String mappings[][] = {
        {"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"}
    };

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        String phone = "3333456789";
        ArrayList list= generateAllnums(phone,"",0);
    }

    private static ArrayList generateAllnums(String phone,String sofar,int j) {
        // TODO Auto-generated method stub

        //System.out.println(phone);
        if(phone.isEmpty()){
            System.out.println(sofar);
            for(int k1=0;k1 list2= generateAllnums(phone.substring(p+1), sofar+phone.charAt(p)+ " ", 0);
            ArrayList list3= generateAllnums(phone.substring(p+1), sofar+phone.charAt(p), 0);

        }
        else{
            ArrayList list1= generateAllnums(phone.substring(1), sofar+phone.charAt(0), 0);
        }
        return null;

    }

}