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

You should check this answer: Getting every possible permutation of a string or combination including repeated characters in Java

To get this code:

public static String[] getAllLists(String[] elements, int lengthOfList)
{

    //lists of length 1 are just the original elements
    if(lengthOfList == 1) return elements; 
    else {
        //initialize our returned list with the number of elements calculated above
        String[] allLists = new String[(int)Math.pow(elements.length, lengthOfList)];

        //the recursion--get all lists of length 3, length 2, all the way up to 1
        String[] allSublists = getAllLists(elements, lengthOfList - 1);

        //append the sublists to each element
        int arrayIndex = 0;

        for(int i = 0; i < elements.length; i++){
            for(int j = 0; j < allSublists.length; j++){
                //add the newly appended combination to the list
                allLists[arrayIndex] = elements[i] + allSublists[j];
                arrayIndex++;
            }
        }
        return allLists;
    }
}

public static void main(String[] args){
    String[] database = {"a","b","c"};
    for(int i=1; i<=database.length; i++){
        String[] result = getAllLists(database, i);
        for(int j=0; j

Although further improvement in memory could be made, since this solution generates all solution to memory first (the array), before we can print it. But the idea is the same, which is to use recursive algorithm.