using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var intCount = 0;

            var intCountIncrement = 1;

            var intPreviousVal = 0;

            var intPreviousIndex = 0;

            var A = new int[] { 4, 8, 8, 12, 15 };

            var listResult = new List<int> { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

​

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

            {

                if (i - 1 > -1) // Get previous value

                {

                    intPreviousVal = A[i - 1];

                }

​

                for (var j = 0; j < listResult.Count; j++)

                {

                    intCount = j + intCountIncrement;

                    intPreviousIndex = listResult.IndexOf(intPreviousVal);

​

                    if (A[i] == listResult[intPreviousIndex]) // Check if previous value is a match

                    {

                        listResult.Insert(intPreviousIndex + 1, A[i]);

                        intCountIncrement--;

                        break;

                    }

                    else if (A[i] == intCount) // Check if A array value matches count

                    {

                        listResult[j] = A[i];

                    }

                }

            }

​

            foreach (var number in listResult)

            {

                Console.WriteLine(number);

            }

    }

}