using System;

public class Program

{

    public static void Main()

    {

        int[] arr = {3, 4, 1, 2, 1, 2, 0, 1, 2, 5, 6};

        int[] srch = {0, 1, 2};

​

        Console.WriteLine(FindLast(arr, srch));

    }

​

    public static int FindLast(int[] haystack, int[] needle)

    {

        // iterate backwards, stop if the rest of the array is shorter than needle (i >= needle.Length)

        for (var i = haystack.Length - 1; i >= needle.Length - 1; i--)

        {

            var found = true;

            // also iterate backwards through needle, stop if elements do not match (!found)

            for (var j = needle.Length - 1; j >= 0 && found; j--)

            {

                // compare needle's element with corresponding element of haystack

                found = haystack[i - (needle.Length - 1 - j)] == needle[j];

            }

            if (found)

                // result was found, i is now the index of the last found element, so subtract needle's length - 1

                return i - (needle.Length - 1);

        }

        // not found, return -1

        return -1;

    }

}