OPPGAVE 1:
----------

================code=====================

public class Permutation{

    // use the entire string as the endingString
    // when called with one parameter
    public void permuteString(String s){
        permuteString("", s);
    }

    public void assignment1(){
        long t_0 = System.currentTimeMillis();
        
        permuteString("123456789");

        System.out.println("time used: "+(System.currentTimeMillis() - t_0)+" ms");
    }

    // recursive declaration of method permuteString
    public void permuteString(
            String beginningString, String endingString ){

        // base case: if string to permute is length less than or equal to
        // 1, just display this string concatenated with beginningString
        if ( endingString.length() <= 1 ){
            if(isDevidable(beginningString + endingString)){
                System.out.println( beginningString + endingString );
            }
        }else{ // recursion step: permute endingString

            // for each character in endingString
            for ( int i = 0; i < endingString.length(); i++ ){
                try{
                    
                    // create new string to permute by eliminating the
                    // character at index i
                    String newEndString = endingString.substring( 0, i ) + endingString.substring( i + 1 );

                    String newBeginString = beginningString + endingString.charAt( i );

                    // recursive call with a new string to permute
                    // and a beginning string to concatenate, which
                    // includes the character at index i

                    if( isDevidable( newBeginString)){
                        permuteString( newBeginString, newEndString );
                    }

                }catch ( StringIndexOutOfBoundsException exception ){
                    exception.printStackTrace();
                }
            } 
        } 
    } 


    public boolean isDevidable(String s){

        // ignore test if string is not a number
        // also ignore for '1' length digits since
        // all numbers % 1 == 0

        if(! s.matches("^\\d+$") || s.length() == 1) return true;

        int sAsInt = Integer.parseInt(s);
        return (sAsInt % s.length() == 0);
    }


    public static void main(String[] args){
        Permutation p = new Permutation(); 
        for(String s: args){
            p.permuteString(s);
            System.out.println("----");
        }

        p.assignment1();
    }
}