Helper method for combining ranges.

CombineRanges.cs

using System;
using System.Collections.Generic;
using Towel.DataStructures;
using static Towel.Statics;

namespace ConsoleApp9001
{
	class Program
	{
		static void Main(string[] args)
		{
			(DateTime, DateTime)[] input = new[]
			{
				(new DateTime(2000, 1, 1), new DateTime(2002, 1, 1)),
				(new DateTime(2000, 1, 1), new DateTime(2009, 1, 1)),
				(new DateTime(2003, 1, 1), new DateTime(2009, 1, 1)),
				(new DateTime(2011, 1, 1), new DateTime(2016, 1, 1)),
			};
			var result = CombineRanges(input);
			foreach (var range in result)
			{
				Console.WriteLine(range);
			}
		}

		/// <summary>Simplifies a sequence of ranges by merging ranges without gaps between them.</summary>
		/// <param name="ranges">The ranges to be simplified.</param>
		/// <returns>A potentially smaller sequence of ranges that have been merged if there were no gaps.</returns>
		static IEnumerable<(T A, T B)> CombineRanges<T>(IEnumerable<(T A, T B)> ranges)
		{
			OmnitreeBoundsLinked<(T A, T B), T> omnitree =
				new(
				((T A, T B) x, out T min1, out T max1) =>
				{
					min1 = x.A;
					max1 = x.B;
				});
			foreach (var (A, B) in ranges)
			{
				bool overlap = false;
				T min = default;
				T max = default;
				omnitree.StepperOverlapped(x =>
					{
						min = !overlap ? x.A : Minimum(min, x.A);
						max = !overlap ? x.B : MaximumValue(max, x.B);
						overlap = true;
					}, A, B);
				if (overlap)
				{
					min = Minimum(min, A);
					max = MaximumValue(max, B);
					omnitree.RemoveOverlapped(min, max);
					omnitree.Add(new(min, max));
				}
				else
				{
					omnitree.Add(new(A, B));
				}
			}
			return omnitree;
		}
	}
}