using System;

using System.Linq;

using System.Collections.Generic;

using System.Diagnostics;

​

public class Program {

    public static void Main() {

        var enumerable = Enumerable.Range( 0, 100000 );

        Console.WriteLine( "Takelast" );

        takelast( enumerable );

        takelast( enumerable );

        takelast( enumerable );

        Console.WriteLine( "Takelast2" );

        takelast2( enumerable );

        takelast2( enumerable );

        takelast2( enumerable );

    }

    private static void takelast( IEnumerable<int> enumerable ) {

        var stop = Stopwatch.StartNew();

        var last3 = enumerable.TakeLast( 10 );

        Console.WriteLine( "Took: " + stop.ElapsedTicks );

        Console.WriteLine( "Last: " + string.Join( ", ", last3 ) );

    }

    private static void takelast2( IEnumerable<int> enumerable ) {

        var stop = Stopwatch.StartNew();

        var last3 = enumerable.TakeLast2( 10 );

        Console.WriteLine( "Took: " + stop.ElapsedTicks );

        Console.WriteLine( "Last: " + string.Join( ", ", last3 ) );

    }

}

​

public static class Extensions {

    /// <summary>

    /// Returns the last <paramref name="n"/> elements.

    /// </summary>

    public static IEnumerable<T> TakeLast<T>( this IEnumerable<T> c, int n ) {

        return c.Reverse().Take( n ).Reverse();

    }

    /// <summary>

    /// Returns the last <paramref name="n"/> elements.

    /// </summary>

    public static IEnumerable<T> TakeLast2<T>( this IEnumerable<T> c, int n ) {

        var count = c.Count();

        return c.Skip( count - n );

    }

}