coin_toss.rb

# https://www.quantamagazine.org/mathematicians-discover-prime-conspiracy-20160313/
#
# If Alice tosses a coin until she sees a head followed by a tail, and Bob tosses a 
# coin until he sees two heads in a row, then on average, Alice will require four tosses 
# while Bob will require six tosses (try this at home!), even though head-tail and head-head 
# have an equal chance of appearing after two coin tosses.

require 'pry'

def toss_coin
	if rand.round == 0
	  coin = "H"
	else
	  coin = "T"
	end
end

@HT_tosses = []
@HH_tosses = []

def check_coin_toss_result(coin_toss_history, person)
	if person == :alice
		if coin_toss_history.last(2).count == 2
			if coin_toss_history.last(2) == ["H", "T"]
				@HT_tosses << coin_toss_history.count
				return true
			else
				return false
			end
		else
			return false
		end
	elsif person == :bob
		if coin_toss_history.last(2).count == 2
			if coin_toss_history.last(2) == ["H", "H"]
				@HH_tosses << coin_toss_history.count
				return true
			else
				return false
			end
		else
			return false
		end
	end
end

def coin_toss_round(person)
	coin_toss_history = []

	check_result = false

	while check_result == false
		coin_toss_history << toss_coin
		check_result = check_coin_toss_result(coin_toss_history, person)
	end

end
# binding.pry
10000.times do |count|
	coin_toss_round(:alice)
	coin_toss_round(:bob)
	printf "\rRound: #{count} Alice (HT average tosses): #{(@HT_tosses.inject{ |sum, el| sum + el }.to_f / @HT_tosses.size).round(2)} Bob (HH average tosses): #{(@HH_tosses.inject{ |sum, el| sum + el }.to_f / @HH_tosses.size).round(2)}"
end

puts ""