using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public class Interval

    {

        // public int Layer { get; set; }

        public int Start { get; set; }

        public int End { get; set; }

    }

    static IEnumerable<Interval> MergeOverlappingIntervals(IEnumerable<Interval> intervals)

    {

        var accumulator = intervals.First();

        intervals = intervals.Skip(1);

​

        foreach (var interval in intervals)

        {

            if (interval.Start == accumulator.End)

            {

                accumulator =  new Interval

                                {

                                    Start = accumulator.Start,

                                    End = interval.End,

                                };

            }

            else

            {

                yield return accumulator;

                accumulator = interval;

            }

        }

​

        yield return accumulator;

    }

​

    public static void Main()

    {

         var input = new[] {

                new Interval { Start = 100, End = 200 },

                new Interval { Start = 200, End = 300 },

                new Interval { Start = 400, End = 500 },

                new Interval { Start = 500, End = 800 },

                new Interval { Start = 900, End = 1100 },

                new Interval { Start = 1300, End = 1500 },

            };

​

        // It's important to order the input on Start

        var orderedIntervals = input.OrderBy(x => x.Start).ToList();

        var mergeResult = MergeOverlappingIntervals(orderedIntervals);

​

        foreach(var item in mergeResult) Console.WriteLine($" Start = {item.Start}, End = {item.End} ");

    }

}