using System;
using System.Linq;
using System.Collections.Generic;

public class Test
{
public class BtnCountViews {
    public int DayOfYear { get; set; }
    public int BtnCount { get; set; }
    public int Views { get; set; }
}
    
    public static void Main() {
        var rnd = new Random();
        List<BtnCountViews> items = Enumerable
            .Range(1, 10)
            .Select(_ => new BtnCountViews {DayOfYear = rnd.Next(20, 200)})
            .ToList();
        items.Sort((x, y) => x.DayOfYear.CompareTo(y.DayOfYear));
        Console.WriteLine("Before: {0}", string.Join(", ", items.Select(x => x.DayOfYear)));
        int i = items.Count-1;
        while (i > 0) {
            if (items[i].DayOfYear == items[i-1].DayOfYear+1) {
                i--;
            } else {
                items.Insert(i, new BtnCountViews { DayOfYear = items[i].DayOfYear-1 });
            }
        }
        Console.WriteLine("After: {0}", string.Join(", ", items.Select(x => x.DayOfYear)));

    }
}