using System;

using System.Collections.Generic;

​

public static class ExtensionExample

{

    // Returns true if the collection contains duplicated data.

    public static bool ContainsDuplicates<T>(this IEnumerable<T> collection, HashSet<T> hashSet)

    {

        hashSet.Clear();

        foreach (var item in collection)

        {

            if (hashSet.Add(item))

                continue;

            return true;

        }

        return false;

    }

}

​

public class Program

{

    private static readonly HashSet<int> m_cachedHashSet = new HashSet<int>();

    public static void Main()

    {

        var uniqueArray = new int[] {0, 1, 2, 3, 4, 5};

        var nonUniqueArray = new int[] {0, 1, 2, 3, 4, 5, 4, 3, 2, 1};

​

        Console.WriteLine(uniqueArray.ContainsDuplicates(m_cachedHashSet));

        Console.WriteLine(nonUniqueArray.ContainsDuplicates(m_cachedHashSet));

    }

}