Card matching game monte carlo

Program.cs

using System.Diagnostics;

const int N_SIMS = 100_000_000;
const int N_THREADS = 1_000;
const int N_PLAYERS = 6;
const int N_WINS = 3;
const int N_PAIRS = 24;
float[] playerAccuracy = [ 0.90f, 0.87f, 0.83f, 0.80f, 0.90f, 0.85f ];

var tasks = Enumerable.Range(0, N_THREADS).Select(i => Task.Run(RunSims)).ToArray();
Stopwatch sw = Stopwatch.StartNew();
Task.WaitAll(tasks);
sw.Stop();

int[] playerWinsTotal = new int[N_PLAYERS];
foreach (var task in tasks) {
    for (int p = 0; p < N_PLAYERS; p++) {
        playerWinsTotal[p] += task.Result[p];
    }
}

Console.WriteLine($"{N_SIMS} runs in {sw.Elapsed.TotalSeconds:f3}s:");
for (int p = 0; p < playerWinsTotal.Length; p++) {
    Console.WriteLine($"\tPlayer {p+1} (acc {playerAccuracy[p]:f2}%): {(double)playerWinsTotal[p] / N_SIMS:p}");
}

int[] RunSims() {
    int[] playerWins = new int[N_PLAYERS];
    for (int i = 0; i < (N_SIMS / N_THREADS); i++) {
        playerWins[RunSim(playerAccuracy)]++;
    }
    return playerWins;
}

static int RunSim(float[] playerAccuracy) {
    Random r = new();
    int[] playerMatches = new int[N_PLAYERS];
    List<int> allCards = Enumerable.Range(0, N_PAIRS * 2).ToList();
    List<int> unknownCards = Enumerable.Range(0, N_PAIRS * 2).ToList();
    HashSet<int> knownHalfPairs = new(N_PAIRS * 2);
    HashSet<(int, int)> knownFullPairs = new(N_PAIRS);

    while (true) {
        for (int p = 0; p < N_PLAYERS; p++) {
            var picks = (-1, -1);
            if (r.NextSingle() > playerAccuracy[p]) { // forgot
                var firstIdx = r.Next(allCards.Count);
                var secondIdx = r.Next(allCards.Count - 1);
                if (secondIdx >= firstIdx) {
                    secondIdx++;
                }
                picks = (allCards[firstIdx], allCards[secondIdx]);
            } else if (knownFullPairs.Count != 0) {
                picks = knownFullPairs.First();
            } else {
                var firstIdx = r.Next(unknownCards.Count);
                picks.Item1 = unknownCards[firstIdx];
                var other = GetOther(picks.Item1);
                if (knownHalfPairs.Contains(other)) {
                    picks.Item2 = other;
                } else {
                    var secondIdx = r.Next(unknownCards.Count - 1);
                    if (secondIdx >= firstIdx) {
                        secondIdx++;
                    }
                    picks.Item2 = unknownCards[secondIdx];
                }
            }

            if (picks.Item1 == GetOther(picks.Item2)) {
                playerMatches[p]++;
                if (playerMatches[p] == N_WINS) {
                    return p;
                }

                allCards.Remove(picks.Item1);
                allCards.Remove(picks.Item2);
                unknownCards.Remove(picks.Item1);
                unknownCards.Remove(picks.Item2);
                knownHalfPairs.Remove(picks.Item1);
                knownHalfPairs.Remove(picks.Item2);
                knownFullPairs.Remove(picks);
                knownFullPairs.Remove((picks.Item2, picks.Item1));
            } else {
                unknownCards.Remove(picks.Item1);
                unknownCards.Remove(picks.Item2);
                var other1 = GetOther(picks.Item1);
                if (knownHalfPairs.Remove(other1)) {
                    knownFullPairs.Add((picks.Item1, other1));
                } else {
                    knownHalfPairs.Add(picks.Item1);
                }
                var other2 = GetOther(picks.Item2);
                if (knownHalfPairs.Remove(other2)) {
                    knownFullPairs.Add((picks.Item2, other2));
                } else {
                    knownHalfPairs.Add(picks.Item2);
                }
            }
        }
    }
}

static int GetOther(int index) {
    return index % 2 == 0 ? index + 1 : index - 1;
}