terras2.rb

def f2(n)
	return n.odd? ? (n * 3 + 1) / 2 : n / 2

end

def re(ns, k)
	n = ns.to_i(2)
	c1 = 0
	w = ''
	k.times { b = n % 2; w << b.to_s; c1 += b; n = f2(n) }
	return n, w, c1
end

def test(msb)
	c = 20
	3.times \
	{
		ns = (1..c).map { rand(2) }.join

		m1, w, c1 = re(msb + '0' + ns, c)

		m2, = re(msb + '1' + ns, c)

		t = 3**c1 == m2 - m1
		p({'a2' => msb, 'b2' => ns, 'm1' => m1, 'm2' => m2, 'Y - X' => m2 - m1, 'w_i' => w, 'n' => c1, '3^n' => 3**c1, '3^n == Y - X' => t})
		raise if (!t)
	}

end


test('1')
test('')
test((1..5).map { rand(2) }.join)