Coin Flip Test

coin.java

import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

public class Main {

	public static void main(String[] args) throws NoSuchAlgorithmException {
		// HT vs HH
		
		// try to mess with this and see the result
		boolean SHOULD_COUNT_CONSECUTIVE_FLIPS = false;

		long occurrenciesHT = 0;
		long totalWaitHT = 0;
		int currentWaitHT = 0;

		long occurrenciesHH = 0;
		long totalWaitHH = 0;
		int currentWaitHH = 0;

		Boolean previousIsTails = false;
		Boolean previousIsHeads = false;

		SecureRandom instanceStrong = SecureRandom.getInstanceStrong();

		for (int i = 0; i < 10000; i++) {
			Boolean isTails = instanceStrong.nextBoolean();
			Boolean isHeads = !isTails;

			System.out.println(isTails ? "T" : "H");

			currentWaitHT++;
			currentWaitHH++;

			// H T and ignore games with just 1 coin flip
			if (previousIsHeads && isTails 
					&& (currentWaitHT > 1 || SHOULD_COUNT_CONSECUTIVE_FLIPS)) {
				occurrenciesHT++;
				totalWaitHT += currentWaitHT;
				System.out.println("HT found!" + currentWaitHT);

				currentWaitHT = 0;
			}

			// H H and ignore games with just 1 coin flip
			if (previousIsHeads && isHeads 
					&& (currentWaitHH > 1 || SHOULD_COUNT_CONSECUTIVE_FLIPS)) {
				occurrenciesHH++;
				totalWaitHH += currentWaitHH;
				System.out.println("HH found!" + currentWaitHH);

				currentWaitHH = 0;
			}

			previousIsTails = isTails;
			previousIsHeads = !previousIsTails;

		}

		System.out.println("occurrenciesHT=" + occurrenciesHT);
		System.out.println("expectedWaitHT=" + ((totalWaitHT + 0.0) / occurrenciesHT));
		System.out.println("occurrenciesHH=" + occurrenciesHH);
		System.out.println("expectedWaitHH=" + ((totalWaitHH + 0.0) / occurrenciesHH));

	}

}