// http://svc.luckstar.com.tw/CodeHelper/cs/index.html
// 2017-03-22, honda@luckstar.com.tw, Create.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleBase
{
    public class CHashSet
    {
        HashSet<string> mList1 = new HashSet<string>();
        public void Run()
        {
            Console.WriteLine("Basic:");
            Console.WriteLine("mList1:");
            mList1.Add("s1");
            mList1.Add("s2");
            mList1.Add("s3");
            if (!mList1.Contains("xxx"))
                mList1.Add("s4");
            if (!mList1.Contains("s4"))
                mList1.Add("s5");

            PrintHashSetS(mList1);

            Console.WriteLine();
            PrintDashLine();
            HashSet<int> evenNumbers = new HashSet<int>();
            HashSet<int> oddNumbers = new HashSet<int>();


            for (int i = 0; i < 5; i++)
            {
                // Populate numbers with just even numbers.
                evenNumbers.Add(i * 2);

                // Populate oddNumbers with just odd numbers.
                oddNumbers.Add((i * 2) + 1);
            }

            Console.Write("evenNumbers contains {0} elements: ", evenNumbers.Count);
            PrintHashSetI(evenNumbers);

            Console.Write("oddNumbers contains {0} elements: ", oddNumbers.Count);
            PrintHashSetI(oddNumbers);

            // Create a new HashSet populated with even numbers.
            HashSet<int> numbers = new HashSet<int>(evenNumbers);
            Console.WriteLine("numbers UnionWith oddNumbers...");
            numbers.UnionWith(oddNumbers);

            Console.Write("numbers contains {0} elements: ", numbers.Count);
            PrintHashSetI(numbers);
        }
        private void PrintHashSetS(HashSet<string> set)
        {
            Console.Write("{");
            foreach (string s1 in set)
            {
                Console.Write(" {0}", s1);
            }
            Console.WriteLine(" }");
        }
        private void PrintHashSetI(HashSet<int> set)
        {
            Console.Write("{");
            foreach (int i in set)
            {
                Console.Write(" {0}", i);
            }
            Console.WriteLine(" }");
        }
        private void PrintDashLine()
        {
            Console.WriteLine();
            Console.WriteLine("----------");
        }
    }
}


result:

Basic:
mList1:
{ s1 s2 s3 s4 }


----------
evenNumbers contains 5 elements: { 0 2 4 6 8 }
oddNumbers contains 5 elements: { 1 3 5 7 9 }
numbers UnionWith oddNumbers...
numbers contains 10 elements: { 0 2 4 6 8 1 3 5 7 9 }