Pakkaus

import java.util.Scanner;

public class Pakkaus {
    
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        //String input = "12fe24he956634ug59456edgbxv";
        String sc = input + "*";
        String s = "";
        String fin = "";
        String[] arr = sc.split("");
        String n = arr[0];
        String t, l=arr[0];
        
        for(int i = 1; i < arr.length; i++)
        {
            t = arr[i];
  
            if(Num(t)) {
                n += arr[i];
            } else if(!Num(t) && !"*".equals(t)) {
                s += arr[i];
            } 
            
            if(Num(t) && !Num(l) || "*".equals(t)) {
                int nn = Integer.parseInt(n);
                fin += repeat(nn, s);
                s = "";
                n = "";
            } 
            l = arr[i];
        }
        System.out.println(fin);
    }

    public static boolean Num(String str) {
            return str.matches("-?\\d+");
    }
    
    public static String repeat(int count, String with) {
        return new String(new char[count]).replace("\0", with);
    }
}

Test 1

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 2

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 3

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 4

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 5

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 6

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 7

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 8

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 9

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 10

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 11

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 12

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 13

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 14

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...

Test 15

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NumberFormatException: For input string: "j0"
	at jav...