using System;

using System.Collections.Generic;

using System.Linq;

​

public class PetCategoryOwner

{

    public string PetCategory { get; set; }

    public string Owner { get; set; }

}

​

public class PetCategoriesOwners

{

    public List<string> PetCategories { get; set; }

    public List<string> Owners { get; set; }

}

public class Program

{

    public static void Main()

    {

        var petCategoryOwner = new List<PetCategoryOwner>()

        {

            new PetCategoryOwner { Owner = "Higa", PetCategory = "Terry"},

            new PetCategoryOwner { Owner = "Higa", PetCategory = "Charlotte"},

            new PetCategoryOwner { Owner = "Oliver", PetCategory = "Terry"},

            new PetCategoryOwner { Owner = "Oliver", PetCategory = "Charlotte"},

            new PetCategoryOwner { Owner = "Oliver", PetCategory = "Chausie"},

            new PetCategoryOwner { Owner = "Price", PetCategory = "Chausie"},

            new PetCategoryOwner { Owner = "Liam", PetCategory = "Terry"},

            new PetCategoryOwner { Owner = "Liam", PetCategory = "Chartreux"}

        };

        var petCategoriesOwners = petCategoryOwner

                .GroupBy(x => x.Owner)

                .Select(x => new

                {

                    Owner = x.Key,

                    Categories = x.Select(y => y.PetCategory)

                })

                .OrderBy(x => x.Categories.Count())

                .Aggregate(new List<PetCategoriesOwners>(), (acc, current) =>

                {

                    var currentCategories = current.Categories.ToList();

                    var matches = acc.Where(group => group.PetCategories.All(x => currentCategories.Contains(x)));

​

                    foreach(var match in matches)

                    {

                        match.Owners.Add(current.Owner);

                        currentCategories = currentCategories.Except(match.PetCategories).ToList();

                    }

​

                    if (currentCategories.Any())

                    {

                        acc.Add(

                            new PetCategoriesOwners() { 

                                Owners = new List<string>() { current.Owner }, 

                                PetCategories = currentCategories 

                            });

                    }

​

                    return acc;

                });

        foreach(var gr in petCategoriesOwners){

            Console.WriteLine(String.Join(",", gr.Owners) + " - " + String.Join(",", gr.PetCategories));    

        }

​

    }

}