using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public class Range {

        public Range(DateTime from, DateTime to) {

            From = from;

            To = to; 

        }

        public DateTime From { get; set; }

        public DateTime To { get; set; }

    }

    public static void Main()

    {

        // set up

        var blockedDates = new[] {

            new DateTime(2015, 11, 10),

            new DateTime(2015, 11, 5),

            new DateTime(2015, 11, 8),

            new DateTime(2015, 11, 6),

            new DateTime(2015, 11, 17),

            new DateTime(2015, 11, 9),

            new DateTime(2015, 11, 14),

            new DateTime(2015, 11, 16),

            new DateTime(2015, 11, 20),

        };

        // create ranges

        var blockedRanges = new List<Range>();

        var blockedRange = (Range)null;

        foreach(var date in blockedDates.OrderBy(d => d)) {

            if (blockedRange == null || blockedRange.To.AddDays(1) != date) {

                blockedRange = new Range(date, date);

                blockedRanges.Add(blockedRange);

            }

            else

                blockedRange.To = date;

        }

        // test

        foreach(var range in blockedRanges)

            Console.WriteLine("from {0:d} to {1:d}", range.From, range.To);

    }

}