using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Scenario1();

    }

    public static void Scenario1()

    {

        var reservations = new[]{

            new Reservation(TimeSpan.FromHours(9), TimeSpan.FromHours(12)),

            new Reservation(TimeSpan.FromHours(10), TimeSpan.FromHours(12)),

            new Reservation(TimeSpan.FromHours(11), TimeSpan.FromHours(12)),

            new Reservation(TimeSpan.FromHours(13), TimeSpan.FromHours(14)) 

        };

        var startTimes = reservations.GroupBy(x => x.StartTime).ToDictionary(k => k.Key, v => v.Count());

        var endTimes = reservations.GroupBy(x => x.EndTime).ToDictionary(k => k.Key, v => v.Count());

​

        var dayStart = TimeSpan.FromHours(8);

        var dayEnd = TimeSpan.FromHours(18);

​

        var currentCount = 0;

        var result = new List<TimeLineItem>();

        var currentStart = dayStart;

        var currentEnd = dayEnd;

        for(var time = dayStart; time<= dayEnd;time = time.Add(TimeSpan.FromMinutes(1)))

        {           

            if(startTimes.TryGetValue(time, out var numStart))

            {               

                if(currentCount>0)

                {   

                    result.Add(CreateItem(currentStart, time, currentCount));

                    currentStart = time;                

                }   

                currentCount += numStart;   

            }

            if(endTimes.TryGetValue(time, out var numEnd))

            {

                if(currentCount>1)

                {   

                    result.Add(CreateItem(currentStart, time, currentCount));

                    currentStart = time;

                }

                currentCount-=numEnd;

            }

        }   

        result.Add(CreateItem(currentStart, dayEnd, currentCount));

        foreach(var item in result)

        {

            Console.WriteLine($"{item.ItemTimeText} ({item.ItemColor})");

        }

    }

    private static TimeLineItem CreateItem(TimeSpan start, TimeSpan end, int count)

    {

        var color = count switch

        {

            <2 => Color.Success,

            2 => Color.Warning,

            _ => Color.Error

        };

        return new TimeLineItem(color, $"{start} - {end}");

    }

}

​

public class Reservation 

{

    public TimeSpan StartTime { get; set; } 

    public TimeSpan EndTime { get; set; }  

​

    public Reservation(TimeSpan startTime, TimeSpan endTime)

    {

        StartTime = startTime;

        EndTime = endTime;

    }

}

​

public class TimeLineItem

{

    public Color ItemColor { get; set; }

    public string ItemTimeText { get; set; }

​

    public TimeLineItem(Color itemColor, string itemTimeText)

    {

        ItemColor = itemColor;

        ItemTimeText = itemTimeText;

    }

}

public enum Color 

{

    Success,

    Warning,

    Error

}