using System;

public class Program

{

    public static void Main()

    {

        // Given an array of integers, write a function that finds all the duplicates in the array. 

        var A = new []{1,2,1,2}; 

        FindDuplicates(A); // expected: [1,2]

        var B = new []{3,3,3}; 

        FindDuplicates(B); // expected: [3]

    }

    internal static int[] FindDuplicates(int[] arr)

    {

        throw new NotImplementedException();

    }

}