Pakkaus

import java.util.Scanner;

public class Pakkaus {
    public static void main(String[] args) { 
        
        final Scanner lukija = new Scanner(System.in);
        
        String syote = lukija.nextLine();
        
        //Jaetaan syote  paloiksi
        StringBuilder purettu = new StringBuilder(0);
        int luku = 0;
        StringBuilder kirjaimet = new StringBuilder();
        boolean kirjainHuomattu = false;
        int arvo = 0;
        
        for (int i = 0; i < syote.length(); i++) {
            //on numero
            arvo = Character.getNumericValue(syote.charAt(i));
            if (arvo < 10) {   
                if (kirjainHuomattu) {
                    for (int a = 0; a < luku; a++) {
                        purettu.append(kirjaimet);
                    }                 
                    luku = 0;
                    kirjaimet.delete(0, kirjaimet.length());
                    kirjainHuomattu = false;
                }
                luku = luku * 10 + arvo; 
            } else {   
                kirjainHuomattu = true;
                kirjaimet.append(syote.charAt(i));
            }
        }
        for (int a = 0; a < luku; a++) {
            purettu.append(kirjaimet);
        } 
        purettu.trimToSize();
        System.out.println(purettu);
    }    
 }

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