using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        int[] arr = new int[] { 1, 2, 3, 4, 5, 0, 0, 0, 0, 7, 8, 9};

        int[] mask = new int[] { 0, 0, 0, 0 };

        int[] subArr = new int[0];

        var start = DateTime.Now;

        var linesToTest = 10000;

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

        {

            subArr = SubArrayTillMask(2, arr, mask);

        }

        //Console.WriteLine(String.Join(",",subArr));

        Console.WriteLine("Tested " + linesToTest + " lines in " + (DateTime.Now - start).TotalSeconds + " seconds");

    }

    static int[] SubArrayTillMask(int start, int[] array, int[] mask ) 

    {

        var foundPos = -1;

        var len = mask.Length;

        var limit = array.Length - len;

        for( var i = 0;  i <= limit;  i++ ) 

        {

            var k = 0;

            for( ;  k < len;  k++ ) {

                if( mask[k] != array[i+k] ) break;

            }

            if( k == len ) foundPos = i;

        }

        if(foundPos == -1)

            return array;

        return array.Skip(start).Take(foundPos-start).ToArray();

    }

}