Bulk Coin Flip Test for r/incremental_games

package com.example;

import static org.apache.commons.math.util.MathUtils.factorialDouble;

public class BulkCoinFlipTest {

    private static boolean myChoose = false;
    private static boolean simulate = true;
    private static boolean memoize = false;
    private static boolean printHistogram = false;

    private static Double[] chanceMemo = null;

    public static void main(String[] args) {
        int periods = 1_000_000;
        double x = 0.2;
        int n = 80;

        // Pre-initialize the math stuff, for clean timing
        for (int i = 0; i < n; i++) {
            try {
                basicXChooseY(n, i);
            } catch (Exception ignore) {}
            myXChooseY(n, i);
        }

        simulate = false;
        runTrial(periods, x, n);

        simulate = true;
//        myChoose = false;
//        runTrial(periods, x, n);

        myChoose = true;
        runTrial(periods, x, n);

        memoize = true;
        runTrial(periods, x, n);
    }

    private static void runTrial(int periods, double x, int n) {
        try {
            System.out.println(periods + " tests of " + n + " rolls with " + (x * 100) + "% chance of success, using " +
                                       (simulate ? (myChoose ? "my" : "the basic") + " choose function and " + (memoize ? "" : "no ") + "memoization"
                                                 : "individual rolls"));
            if (memoize) chanceMemo = new Double[n];
            int[] hist = new int[n + 1];
            long start = System.currentTimeMillis();
            for (int i = 0; i < periods; i++) {
                hist[getSuccesses(x, n)]++;
            }
            long elapsed = System.currentTimeMillis() - start;
            System.out.println("Elapsed time (ms): " + elapsed);
            if (printHistogram) printHistogram(hist, periods);
        } catch (Exception e) {
            System.out.println(e.toString());
        }
        System.out.println();
    }

    static int getSuccesses(double x, int n) {
        return simulate ? getSimulatedSuccesses(x, n) : getRealSuccesses(x, n);
    }

    static int getSimulatedSuccesses(double x, int n) {
        double roll = Math.random();
        int result = 0;
        double chance = getChanceOfMSuccesses(x, n, result);
        while (chance < roll) {
            roll -= chance;
            result++;
            chance = getChanceOfMSuccesses(x, n, result);
        }
        return result;
    }

    static int getRealSuccesses(double x, int n) {
        int result = 0;
        for (int i = 0; i < n; i++) {
            if (Math.random() < x) result++;
        }
        return result;
    }

    static double getChanceOfMSuccesses(double x, int n, int m) {
        if (memoize) {
            if (chanceMemo[m] != null) return chanceMemo[m];
            return chanceMemo[m] = Math.pow(x, m) * Math.pow(1 - x, n - m) * xChooseY(n, m);
        } else {
            return Math.pow(x, m) * Math.pow(1 - x, n - m) * xChooseY(n, m);
        }
    }

    static double xChooseY(int x, int y) {
        if (myChoose) return myXChooseY(x, y);
        else return basicXChooseY(x, y);
    }

    static double basicXChooseY(int x, int y) {
        if (x > 170 || y > 170) throw new IllegalArgumentException("Too large for factorial calculation");
        return factorialDouble(x) / (factorialDouble(y) * factorialDouble(x - y));
    }

    static double myXChooseY(int x, int y) {
        if (2*y >= x) {
            double result = 1;
            for (int i = x; i > y; i--) {
                result *= i;
            }
            return result / factorialDouble(x-y);
        } else {
            return myXChooseY(x, x-y);
        }
    }

    // Useful for comparing results between methods for correctness
    static void printHistogram(int[] hist, int n) {
        System.out.println("Successes: periods\n");
        int digits = new Double(Math.log10(n)).intValue() + 1;
        int idigits = new Double(Math.log10(hist.length)).intValue() + 1;
        for (int i = 0; i < hist.length; i++) {
            System.out.printf("%" + idigits + "d: %" + digits + "d\n", i, hist[i]);
        }
    }
}