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def gcd(a, b)
	if a == 0  
		return b
	elsif b == 0
		return a
	else
		q = a / b
		r = a % b
		a = b
		b = r
		gcd(a, b)
	end
end

puts gcd(270, 192)
puts gcd(192, 270)

def binary(num)
	int = []
	i = 0
	q = num
	while q > 0
		int[i] = q % 2
		q = q / 2
		i += 1
	end
	int.reverse!
end

def mod_exponent(base, exponent: exp, mod: mod)
	binary = binary(exponent).reverse!
	output = []
	temp = 0

	binary.each_with_index do |element, ind| 
		value = 2 ** ind
		temp = value == 1 ? temp = (base * value) % mod : temp = (temp * temp) % mod
		output << temp if element != 0
	end

	product = output.inject(1) { |product, element| product * element }
	mod_exp = product % mod
end

puts "binary of 1234 = #{binary(1234)}"
puts mod_exponent(98765, exponent: 1234, mod: 123557)

class PrimeNumber
	def initialize(num)
		@num = num + 1
		@composite = Array.new(@num, 0)
		@composite[0] = 1
		@composite[1] = 1
		@primes = []
	end

	def sieve
		sr = Math.sqrt(@num).ceil
		sr.times do |index|
			if @composite[index] != 1
				start = index * index
				while start < @num 
					@composite[start] = 1
					start += index
				end
			end
		end
		@composite.each_with_index do |num, index| 
			@primes << index if num != 1
		end
		@primes
	end
end

prime = PrimeNumber.new(100)
puts prime.sieve