package basepkg;

import java.util.TreeSet;
import java.util.Set;

public class MainForPermutation {

      public Set<String> permute(String str){
        //Using a set will get rid of duplicates
        Set<String> set = new TreeSet<String>();
        // Condition for termination
        if (str.length() == 1){
                set.add(str);
        }else{
            // Removes the character at index i
            for (int i=0; i<str.length(); i++){
                String pre = str.substring(0, i);
                String post = str.substring(i+1);
                String remaining = pre+post;
            // Concatenation process of remainder characters
            for (String permutation : permute(remaining)){
                set.add(str.charAt(i) + permutation);
            }
          }
        }
        return set;
      }

      public static void main(String[] args) throws IllegalArgumentException{

      MainForPermutation mainClass;
      String exThrown="Exception has occured, reason : ";
      // throws exception if argument is null :: command line
        if (args.length <= 0){
            System.err.println(exThrown+"NULL argument passed on");
            throw new IllegalArgumentException();
        }

      mainClass = new MainForPermutation();

        for (int i =0;i<args.length;i++){

            if (args[i].matches("^[A-Za-z0-9]+$")){
                System.out.println(mainClass.permute(args[i]));
                // prints on console, sorted permuted characters
            }else{
                System.err.println(exThrown+"Invalid chars in string");
                throw new IllegalArgumentException();
                  // throws exception if argument is not alphanumeric  (~#@*+%{}<>[]|“”\_^) not allowed
            }
        }
      }

/*    Expected result set  (https://www.codeeval.com/public_sc/14/)

      aht,ath,hat,hta,tah,tha
      abc,acb,bac,bca,cab,cba
      6Zu,6uZ,Z6u,Zu6,u6Z,uZ6   */

}