Computes expected number of packs required to complete a portion of your collection in Hearthstone

PackStatistics.java

package me.dphil.statistics

import java.util.Random;
import java.util.concurrent.TimeUnit;

/**
 * Many people have written this before and many will write it again. I
 * wrote it because it was faster than looking for someone else's solution.
 */
public class PackStatistics {
    private static final int NUM_BUCKETS = 36;
    private static final int FULL_BUCKET_SIZE = 2;
    private static final int REQUIRED_FULL_BUCKETS = 32;
    private static final int NUM_SIMULATIONS = 100000;

    public static void main(String[] args) {
        long startTime = System.nanoTime();
        int[] results = new int[NUM_SIMULATIONS];
        for (int i = 0; i < NUM_SIMULATIONS; i++) {
            results[i] = simulateOnce();
        }
        int sum = 0;
        for (int i = 0; i < NUM_SIMULATIONS; i++) {
            sum += results[i];
        }
        double mean = (double)sum / NUM_SIMULATIONS;
        double squaredDifferenceSum = 0;
        for (int i = 0; i < NUM_SIMULATIONS; i++) {
            double difference = results[i] - mean;
            squaredDifferenceSum += difference * difference;
        }
        double standardDeviation =
                Math.sqrt(squaredDifferenceSum / NUM_SIMULATIONS);
        long endTime = System.nanoTime();
        System.out.println("Mean: " + mean);
        System.out.println("Standard deviation: " + standardDeviation);
        System.out.println("Computation time: "
                + TimeUnit.NANOSECONDS.toMillis(endTime - startTime) + "ms");
    }

    private static int simulateOnce() {
        Random random = new Random();
        int[] buckets = new int[NUM_BUCKETS];
        int tries = 0;
        int unfilledBuckets = REQUIRED_FULL_BUCKETS;
        while (unfilledBuckets > 0) {
            tries ++;
            int nextBucket = random.nextInt(NUM_BUCKETS);
            int bucketValue = ++buckets[nextBucket];
            if (bucketValue == FULL_BUCKET_SIZE) {
                unfilledBuckets--;
            }
        }
        return tries;
    }
}