MergeIntervals.cs

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

namespace MergeIntervals
{
    class Program
    {
        public static IList<Interval> Merge(IList<Interval> intervals)
        {
            Queue<Interval> solutionStack = new Queue<Interval>();
            intervals = intervals.OrderBy(x => x.start).ToList();

            foreach (var item in intervals)
            {
                if(solutionStack.Count == 0)
                {
                    solutionStack.Enqueue(item);
                }
                else
                {
                    var peek = solutionStack.Last();
                    if(peek.end>= item.start)
                    {
                        peek.end = item.end > peek.end ? item.end : peek.end;
                    }
                    else
                    {
                        solutionStack.Enqueue(item);
                    }
                }
            }

            return solutionStack.ToList();

        }

        static void Main(string[] args)
        {
            var collection = new List<Interval>()
            {
                new Interval() { start = 1, end = 4 },
                new Interval() { start = 2, end = 3 }
            };

            var result = Merge(collection);

            foreach (var item in result)
            {
                System.Console.WriteLine($"[{item.start}, {item.end}]");
            }
        }
    }

    public class Interval
    {
        public int start { get; set; }
        public int end { get; set; }
    }
}