using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        List<Time> availableTimes = new List<Time>

        {

            new Time { From = new DateTime(2018, 1, 15), To = new DateTime(2018, 1, 19), ResourceId = 1 },

            new Time { From = new DateTime(2018, 1, 15), To = new DateTime(2018, 1, 16), ResourceId = 2 },

            new Time { From = new DateTime(2018, 1, 16), To = new DateTime(2018, 1, 19), ResourceId = 3 },

            new Time { From = new DateTime(2018, 1, 15), To = new DateTime(2018, 1, 19), ResourceId = 4 },

            new Time { From = new DateTime(2018, 1, 16), To = new DateTime(2018, 1, 17), ResourceId = 5 },

            new Time { From = new DateTime(2018, 1, 17), To = new DateTime(2018, 1, 18), ResourceId = 2 },

            new Time { From = new DateTime(2018, 1, 17), To = new DateTime(2018, 1, 18), ResourceId = 5 },

            new Time { From = new DateTime(2018, 1, 16), To = new DateTime(2018, 1, 18), ResourceId = 6 },

            new Time { From = new DateTime(2018, 1, 18), To = new DateTime(2018, 1, 19), ResourceId = 2 },

            new Time { From = new DateTime(2018, 1, 15), To = new DateTime(2018, 1, 19), ResourceId = 7 },

        };

        int numberOfResourcesToBook = 2;   // change this to play with it -- try 1, 2, 3, and 4

        var result = availableTimes

            .GroupBy(l => new { l.From, l.To })

            .Select(g => new

            {

                Date = g.Key,

                Count = g.Select(l => l.ResourceId).Distinct().Count(),

                Times = g.Select(l => l)

            })

            .Where(c => c.Count >= numberOfResourcesToBook);

        bool enoughResourceAvailable = result.Any();

        var allMatchingTimes = result.SelectMany(c => c.Times);

​

        Console.WriteLine("Enough resources available: " + (enoughResourceAvailable ? "Yes" : "No"));

​

        Console.WriteLine("\nGroups with counts:");

        foreach (var t in result)

            Console.WriteLine(string.Format("{0} {1} - {2} resources", t.Date.From.ToShortDateString(), t.Date.To.ToShortDateString(), t.Count));

        Console.WriteLine("\nMatching items from original list:");

        foreach (var t in allMatchingTimes)

            Console.WriteLine(string.Format("{0} {1} {2}", t.From.ToShortDateString(), t.To.ToShortDateString(), t.ResourceId));

    }

}

​

class Time

{

    public DateTime From { get; set; }

    public DateTime To { get; set; }

    public int ResourceId { get; set; }

}

​