Järjestys

import java.util.Scanner;
import static java.lang.System.arraycopy;
import java.util.Arrays;
import java.util.Collections;
 
public class Jarjestys {
 
    static int[] arr /*= {4, 5, 2, 7, 8, 1, 9, 6, 3}*/;
    static int n;
    
    public static void main(String[] args) {
        
//        n = arr.length;
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        
        int[] arr = new int[n];
        
        for(int i : arr)
        {
            arr[i] = scan.nextInt();
        }
        
        String fin = "";
 
        for(int i = n; i > 0; i--)
        {
            fin += finder(i) + " ";
        }
        System.out.println(n);
        System.out.println(fin);
    }
    
    public static int[] swap(int n2, int[] arr, int p)
    {
        int a = n2-(p+1); 
        int[] arr2 = new int[n2];
        int[] arr3 = new int[a];
        arraycopy(arr, 0, arr2, a, p+1);
        arraycopy(arr, p+1, arr3, 0, a);
        Collections.reverse(Arrays.asList(arr3));
        arraycopy(arr3, 0, arr2, 0, a);
        return arr2;
    }
    
    static int finder(int i)
    {
        for(int j = 0; j < i; j++)
        {
            if(arr[j] == i)
            {
                arr = swap(i ,arr, j);
                return j+1;
            }       
        }
        return 0;
    }
}

Test 1

Group: 1

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NullPointerException
	at Jarjestys.finder(Jarjestys.java:50)
	at Jarjestys.main(Jarjestys.java:28)

Test 2

Group: 2

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NullPointerException
	at Jarjestys.finder(Jarjestys.java:50)
	at Jarjestys.main(Jarjestys.java:28)

Test 3

Group: 3

Verdict: RUNTIME ERROR

Exception in thread "main" java.lang.NullPointerException
	at Jarjestys.finder(Jarjestys.java:50)
	at Jarjestys.main(Jarjestys.java:28)