using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

            char[] firstSequence = new char[] { 'A', 'B', 'C', 'D'};

            char[] secondSequence = new char[] {'X','A','Z','A','B','C','D','E','A'};

            string firstString = new string(firstSequence);

            string secondString = new string(secondSequence);

            bool isExist = secondString.Contains(firstString);

            Console.WriteLine(isExist ? "Sequence Exist" : "Sequence Not Exist");

            if(isExist)

            {   

                var startIndex = secondString.IndexOf(firstString); 

                Console.WriteLine(string.Join(",", Enumerable.Range(startIndex, firstString.Length)));

            }

    }

}