public static void main(){
        String input = "abcdef";
        for(int i = 1; i < input.length(); i++)
        {
            FindSubsetsOfLength(input, i, "", i);
        }
    }

    public static void FindSubsetsOfLength(String input, int l, String prefix, int desiredLength)
    {
        // If it is possible to find a subset of length l in this prefix:
        if(input.length() > l) {

            // Case 1: Exclude the first character in input
            if(input.length() > l && l > 0){
                FindSubsetsOfLength(input.substring(1), l, prefix, desiredLength);
            }

            // Case 2: include the first character in input
            String newPrefix = prefix + input.charAt(0);
            FindSubsetsOfLength(input.substring(1), l-1, newPrefix, desiredLength);
        }
        // Otherwise, if it is not possible to find a subset of length l in this prefix:
        else if (prefix.length() == desiredLength) {
            System.out.println(prefix);
        }

    }