using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var projects = new List<Project> {

            new Project("P1", DateTime.Parse("12/21/2017"), DateTime.Parse("01/20/2018")),

            new Project("P2", DateTime.Parse("12/01/2017"), DateTime.Parse("12/21/2017")),

            new Project("P3", DateTime.Parse("10/25/2017"), DateTime.Parse("12/01/2017")),

            new Project("P4", DateTime.Parse("09/17/2017"), DateTime.Parse("10/25/2017")),

            new Project("P5", DateTime.Parse("08/01/2017"), DateTime.Parse("09/02/2017")),

            new Project("P6", DateTime.Parse("06/25/2017"), DateTime.Parse("07/26/2017")),

            new Project("P7", DateTime.Parse("04/20/2017"), DateTime.Parse("06/25/2017")),

        };

        Console.WriteLine(projects.Aggregate<Project, string>(string.Empty, (s, p) => $"{p.ToString()}\n{s}"));

        projects = Consolidate(projects);

        Console.WriteLine(projects.Aggregate<Project, string>(string.Empty, (s, p) => $"{p.ToString()}\n{s}"));

​

        projects = new List<Project> {

            new Project("P1", DateTime.Parse("12/21/2017"), DateTime.Parse("01/20/2018")),

            new Project("P2", DateTime.Parse("12/01/2017"), DateTime.Parse("12/21/2017")),

            new Project("P3", DateTime.Parse("10/25/2017"), DateTime.Parse("12/01/2017")),

            new Project("P4", DateTime.Parse("09/17/2017")),

            new Project("P5", DateTime.Parse("08/01/2017"), DateTime.Parse("09/02/2017")),

            new Project("P6", DateTime.Parse("06/25/2017")),

            new Project("P7", DateTime.Parse("04/20/2017"), DateTime.Parse("06/25/2017")),

        };

        Console.WriteLine(projects.Aggregate<Project, string>(string.Empty, (s, p) => $"{p.ToString()}\n{s}"));

        projects = Consolidate(projects);

        Console.WriteLine(projects.Aggregate<Project, string>(string.Empty, (s, p) => $"{p.ToString()}\n{s}"));

    }

    private static List<Project> Consolidate(List<Project> projects)

    {

        var result = new List<Project>();

        // if empty return

        if (!projects.Any()) return result;

​

        // adding first project to a new list

        // and removing it from the main list

        result.Add(projects.First());

        projects.Remove(projects.First());

        // loop over all projects in the main list

        projects.ForEach(p =>

        {

            // checking if any of the projects in the new list

            // starts on the same date as the end date of the

            // current project

            if (result.Any(r => r.BeginDate == (p.EndDate.HasValue ? p.EndDate.Value : DateTime.Today) && r.Name != p.Name))

            {

                // if you find any get it

                var match = result.First(r => r.BeginDate == (p.EndDate.HasValue ? p.EndDate.Value : DateTime.Today));

                var index = result.IndexOf(match);

                // create new project that consalidate both projects

                result[index] = new Project(match.Name, p.BeginDate, match.EndDate);

            }

            else

            {

                // if didn't find any add the current 

                // project to the new list

                result.Add(p);

            }

        });

​

        return result;

    }

}

​

public class Project

{

    public Project(string name, DateTime beginDate) : this(name, beginDate, null) { }

    public Project(string name, DateTime beginDate, DateTime? endDate)

    {

        Name = name;

        BeginDate = beginDate;

        EndDate = endDate;

    }

​

    public string Name { get; set; }

    public DateTime BeginDate { get; set; }

    public DateTime? EndDate { get; set; }

​

    public override string ToString()

    {

        return $"{Name}:\t{BeginDate.ToShortDateString()}\t:\t{(EndDate.HasValue ? EndDate.Value.ToShortDateString() : "Present")}";

    }

}