Smart way to generate permutation and combination of String

Question

String database[] = {\'a\', \'b\', \'c\'};

I would like to generate the following strings sequence, based on given database.

Answer 1

i came across this question as one of the interview question. Following is the solution that i have implemented for this problem using recursion.

public class PasswordCracker {

private List doComputations(String inputString) {

    List totalList =  new ArrayList();
    for (int i = 1; i <= inputString.length(); i++) {

        totalList.addAll(getCombinationsPerLength(inputString, i));
    }
    return totalList;

}

private ArrayList getCombinationsPerLength(
        String inputString, int i) {

    ArrayList combinations = new ArrayList();

    if (i == 1) {

        char [] charArray = inputString.toCharArray();
        for (int j = 0; j < charArray.length; j++) {
            combinations.add(((Character)charArray[j]).toString());
        }
        return combinations;
    }
    for (int j = 0; j < inputString.length(); j++) {

        ArrayList combs = getCombinationsPerLength(inputString, i-1);
        for (String string : combs) {
            combinations.add(inputString.charAt(j) + string);
        }
    }

    return combinations;
}
public static void main(String args[]) {

    String testString = "abc";
    PasswordCracker crackerTest = new PasswordCracker();
    System.out.println(crackerTest.doComputations(testString));

}
}