using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Write(Commoms(new int[] {1, 8, 3, 2},new int[]  {4, 2, 6, 1}));//   {1, 2}

Write(Commoms(new int[] {1, 8, 3, 2, 6}, new int[]{2, 6, 1}));//    {2, 6, 1}

Write(Commoms(new int[] {1, 3, 7, 9}, new int[]{7, 1, 9, 3}));//    {1, 3, 7, 9}

Write(Commoms(new int[] {1, 2}, new int[]{3, 4}));//    {}

Write(Commoms(new int[] {}, new int[]{1, 2, 3}));// {}

Write(Commoms(new int[] {1, 2},new int[] {}));//    {}

Write(Commoms(new int[] {1, 2}, null));//   null

Write(Commoms( null, new int[]{}));

Write(Commoms(null, null));

    } 

    public static void Write(int [] a)

    {

        if(a == null)

        {

            Console.WriteLine("null");

            return;

        }

        if(a.Length == 0)

        {

            Console.WriteLine("0");

            return;

        }

        foreach(int i in a)

        {

            Console.Write(i.ToString() + " ");

        }

        Console.WriteLine();

    }

    public static int[] Commoms(int []f1, int []f2)

    {

        if(f1 == null || f2 == null)

            return null;

        int min = f1.Length > f2.Length ? f2.Length : f1.Length;

        var retVal = new int[min];

        if(f1.Length== 0 || f2.Length== 0 )

            return retVal;

        int k = 0;

        for(int i = 0; i < f1.Length; i++)

        {

            for(int j = 0; j < f2.Length; j++)

            {

                if(f1[i] == f2[j])

                {

                    retVal[k] = f1[i];

                    k++;

                }

            }

        }

        int[] r = new int[k];

        for(int i = 0; i < k; i++)

        {

            r[i]= retVal[i];

        }

        return r;

    }

}