/*

The HashSet<T> class provides high-performance set operations. 

A set is a collection that contains no duplicate elements, and whose elements are in no particular order.

No element look up, can't use index

*/

using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

    var bigCities = new HashSet<string> ()

            //var bigCities = new HashSet<string> (StringComparer.InvariantCultureIgnoreCase)// will ignore case

            { "New York", "Manchester", "Sheffield", "Paris" };

​

            bool addedSheffield = bigCities.Add("Sheffield");// cannot add same

            bool addedsheffield = bigCities.Add("sheffield");//  added becoz of  case difference

            bool addedBeijing = bigCities.Add("Beijing");

            Console.WriteLine("Added Sheffield? " + addedSheffield);

            Console.WriteLine("Added sheffield? " + addedsheffield);

            Console.WriteLine("Added Beijing? " + addedBeijing);

            Console.WriteLine();

​

            foreach (string city in bigCities)

                Console.WriteLine(city);

        setMethods();

    }

    public static void setMethods(){

    var bigCities = new HashSet<string> 

            { "New York", "Manchester", "Sheffield", "Paris" };

​

            string[] citiesInUk = 

            { "Sheffield", "Ripon", "Truro", "Manchester" };

​

            // using LINQ

            var newCities = bigCities.Intersect(citiesInUk);

            foreach (string city in newCities)

                Console.WriteLine(city);

            Console.WriteLine();

​

            // using ISet<T> methods

            // uncomment the operation you want

            bigCities.IntersectWith(citiesInUk);

            //bigCities.UnionWith(citiesInUk);

            //bigCities.SymmetricExceptWith(citiesInUk);

            //bigCities.ExceptWith(citiesInUk);

            foreach (string city in bigCities)

                Console.WriteLine(city);

    }

}