Opening hand simulator

Program.cs

using System.Diagnostics;

const int deckSize = 60;
const int sampleHandsCount = 3;
const int openingHandsCards = 7;
const int simulateTimes = 10_000_000;

Console.WriteLine("Opening hand simulator v1.0");
Console.WriteLine($" @deckSize: {deckSize}, @sampleHandsCount: {sampleHandsCount}, @openingHandsCards: {openingHandsCards}");
Console.WriteLine($" @simulateTimes: {simulateTimes}");
Console.WriteLine($"");

var rand = new Random();
var stopwatch = new Stopwatch();
stopwatch.Start();
foreach (var l in Enumerable.Range(20, 10))
{
    SimulateDeck(deckSize, l);
}
stopwatch.Stop();
Console.WriteLine($"({stopwatch.Elapsed.TotalMilliseconds}ms.)");

// 規定数の初手を生成し、期待値に一番近かった初手の土地の枚数を返す
char SimulateOnce(ReadOnlySpan<bool> deck, double expectedLandsCount)
{
    char candidate = (char)0;
    double lastDiff = double.PositiveInfinity;
    for (int i = 0; i < sampleHandsCount; i++)
    {
        var lands = SimulateOpeningHand(deck);
        var diff = Math.Abs(lands - expectedLandsCount);
        if (diff < lastDiff)
        {
            lastDiff = diff;
            candidate = lands;
        }
    }
    
    return candidate;
}

// 初手1回分の土地の枚数を返す 
char SimulateOpeningHand(ReadOnlySpan<bool> deck)
{
    Span<char> buf = stackalloc char[openingHandsCards];
    var count = 0;
    while (count < openingHandsCards)
    {
        int idx;
        lock (rand)
        {
            idx = rand.Next(59);
        }

        var dup = false;
        for (var cur = 0; cur < count; cur++)
        {
            if (buf[cur] == idx)
            {
                dup = true;
                break;
            }
        }

        if (!dup)
        {
            buf[count++] = (char)idx;
        }
    }

    char landsCount = (char)0;
    for (int i = 0; i < openingHandsCards; i++)
    {
        if (deck[buf[i]])
        {
            landsCount++;
        }
    }
    
    return landsCount;
}

void SimulateDeck(int deckCards, int lands)
{
    var ratio = GetExpectedCount(deckCards, lands);
    Console.WriteLine($"=== simulate {lands}/{deckCards} lands ({ratio:F2} lands expected) ===");
    var deck = Enumerable.Repeat(true, lands).Concat(Enumerable.Repeat(false, deckCards - lands)).ToArray();
    char[] result = new char[simulateTimes];

    for (int i = 0; i < simulateTimes; i++)
    {
        result[i] = SimulateOnce(deck, ratio);
    }
    
    var grouped = result.GroupBy(l => l).OrderBy(l => l.Key).ToList();
    var max = grouped.MaxBy(l => l.Count()).Key;
    
    foreach (var n in Enumerable.Range(0, 8))
    {
        Console.Write(n == max ? "*" : " ");
        var r = grouped.FirstOrDefault(g => g.Key == n);
        var count = r?.Count() ?? 0;
        var percentage = ((count / (double)simulateTimes) * 100).ToString("F2").PadLeft(6);
        Console.WriteLine($"{n}: {percentage}%");
    }
}

double GetExpectedCount(int deckCards, int lands)
{
    var deck = Enumerable.Repeat(true, lands).Concat(Enumerable.Repeat(false, deckCards - lands)).ToArray();
    char[] buf = new char[simulateTimes];

    for (int i = 0; i < simulateTimes; i++)
    {
        buf[i] =SimulateOpeningHand(deck);
    }
    
    var expected = buf.Average(c => c);
    return ((int)(expected*1000)) / 1000.0;
}