Pakkaus

import java.util.Arrays;
import java.util.Objects;
import java.util.Scanner;

/**
 *
 * @author Roni Juntunen
 */

public class Pakkaus {
    public static void main(String[] args) {
        //Nyt on paras olla nopee, kun kaikki stringit on muutettu char arrayksi
        //long[] time = new long[6]; //ajan testaamiseen vain debugaukseen
        Scanner input = new Scanner(System.in);
        //while(System.in.available() == 0){}
        char[] in = input.next().toCharArray(); //luetaan parametrit merkkijonoon
        //time[0] = System.currentTimeMillis();
        char[] out = new char[1000000]; //varataan muuttuja tulokselle
        int indexin = 0; //ilmaisee merkkijonon luennan sijainnin
        int indexout = 0; //ilmaisee merkkijonon ulostulon sijainnin
        int end = in.length; //merkkijonon pituus
        int multiplier = 0; //valmis kerroin
        char[] subchars = new char[1000000]; //toistettava merkkijono
        boolean loop = true; //niin kauan kuin true, ohjelma pyorii
        int size;
        while (loop){ //main loop
            size = 0;
            while (Character.isDigit(in[indexin])){ //luetaan kerroin
                multiplier = multiplier * 10 + Character.getNumericValue(in[indexin]);
                indexin++;
                size++;
            }
            size = 0;
            do { //luetaan merkkijono
                size++;
                subchars[size - 1] = in[indexin];
                indexin++;
                if (Objects.equals(indexin, end)){
                    loop = false;
                    break;
                }
            } while (Character.isLetter(in[indexin]));
            for (int i = 0; i < multiplier; i++) {
                System.arraycopy(subchars, 0, out, indexout + i * size, size);
            }
            indexout += multiplier * size;
            multiplier = 0;
            //out[multiplier / end * 1000] += String.valueOf(new char[multiplier]).replace("\0", substring); //toistetaan merkkijono kertoimen mukaan
            //char c[] = (String.valueOf(new char[multiplier]).replace("\0", substring)).toCharArray();
            //System.arraycopy(c, 0, out, indexout, multiplier * substring.length());
            //indexout += multiplier * substring.length();
            //String s = String.valueOf(new char[multiplier]).replace("\0", substring); //toistetaan merkkijono kertoimen mukaan
            //out += String.valueOf(new char[multiplier]).replace("\0", substring); //toistetaan merkkijono kertoimen mukaan
            //for (int i = 0; i < multiplier; i++) {
                //out = out + substring;
            //}
            }
        //time[1] = System.currentTimeMillis();
        System.out.println(Arrays.toString(out).replaceAll("\\W","")); //tulostetaan tulos
        //System.out.println(time[1] - time[0] + 300); //tulostetaan aika
    }
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED