using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        // input: [['Casper', 'Purple', 'Wayfair'], ['Purple', 'Wayfair', 'Tradesy'], ['Wayfair', 'Tradesy', 'Peleton']]

        // output: {

        // 'Casper': ['Purple', 'Wayfair'],

        // 'Purple': ['Wayfair'],

        // 'Wayfair': ['Purple', 'Tradesy'],

        // 'Peleton': ['Wayfair', 'Tradesy'],

        //}

        var input = new List<List<String>>();

        input.Add(new List<String>()

        {"Casper", "Purple", "Wayfair"});

        input.Add(new List<String>()

        {"Purple", "Wayfair", "Tradesy"});

        input.Add(new List<String>()

        {"Wayfair", "Tradesy", "Peleton"});

        CreateRecomendation(input);

    }

​

    static Dictionary<String, List<String>> CreateRecomendation(List<List<String>> orders)

    {

        var answer = new Dictionary<String, List<String>>();

        var products = new Dictionary<String, Dictionary<String, int>>();

        orders.ForEach(x => x.ForEach(y =>

        {

            if (!products.ContainsKey(y))

                products.Add(y, new Dictionary<String, int>());

        }));

        orders.ForEach(x =>

        {

            foreach (var product in products)

            {

                if (x.Contains(product.Key))

                {

                    x.ForEach(y =>

                    {

                        if (product.Key == y)

                            return;

                        if (!products[product.Key].ContainsKey(y))

                            products[product.Key].Add(y, 1);

                        else

                            products[product.Key][y] += 1;

                    });

                }

            }

        });

        foreach (var product in products)

        {

            Console.WriteLine(product.Key);

            foreach (var item in products[product.Key])

                Console.WriteLine(item.Key + " => " + item.Value);

            Console.WriteLine("---");

        }

​

        return answer;

    }

}