Get kpc

 

import java.util.ArrayList;

public class GetKpc {
    static String[] codes = {".;", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tu", "vwx", "yz"};

    public static void main(String[] args) {
        String str = "12";
        ArrayList<String> ans = getKPC(str);
        System.out.println(ans);
    }

    private static ArrayList<String> getKPC(String str) {
        // base case
        if (str.length() == 0) {
            ArrayList<String> rem = new ArrayList<>();
            rem.add("");
            return rem;
        }

        int firstNum = str.charAt(0) - '0';
        String firstValue = codes[firstNum];

        String remString = str.substring(1);

        // faith
        ArrayList<String> faith = getKPC(remString);

        // expectation meet faith
        ArrayList<String> ans = new ArrayList<>();
        for (String f : faith) {
            for (int i = 0; i < firstValue.length(); i++) {
                ans.add(firstValue.charAt(i) + f);
            }
        }

        return ans;
    }

}