using System;

using System.Linq;

using System.Collections.Generic;

using System.Diagnostics;

​

public class Program

{

    public static IEnumerable<int> AlternatingSequence()

    {

        var i = 1;

        yield return i;

        var b = false;

        while (true)

            yield return ((b = !b) ? -1 : 1) * (i = i + 2);

    }

​

    public static double EstimatePI(int sumLength)

    {

        return (4 * AlternatingSequence().Take(sumLength).Sum(x => 1.0 / x));

    }

    public static double SolveUsingLinq()

    {

        return EstimatePI(1000000);

    }

​

    public static double SolveUsingLoop()

    {

        double t = 0.0;

        for(int i = 1, m = 1, c=0; c < 1000000; i+=2,m*=-1,++c) {

           t += (1.0/i)*m;  

        }

        return t;

    }

    const int NumberOfTries=30;

    public static int Main()

    {

        Stopwatch stopwatch = new Stopwatch();

        long s = 0;

        for(int i = 0; i < NumberOfTries; ++i)

        {

            stopwatch.Restart();

            double pi1 = SolveUsingLinq();

            stopwatch.Stop();

            s += stopwatch.ElapsedMilliseconds;

​

        }

        Console.WriteLine("SolveUsingLinq: average time taken = {0}", s/NumberOfTries);

        s = 0;

        for(int i = 0; i < NumberOfTries; ++i)

        {

            stopwatch.Restart();

            double pi2 = SolveUsingLoop();

            stopwatch.Stop();

            s += stopwatch.ElapsedMilliseconds;

​

        }

        Console.WriteLine("SolveUsingLoop: average time taken = {0}", s/NumberOfTries);

        return 0;

    }

}