Inverse FizzBuzz in Ruby

エレガンスからは程遠いですが..

# Inverse FizzBuzz
def fizzbuzz(n)
  x = ""
  x << "Fizz" if n%3 == 0
  x << "Buzz" if n%5 == 0
  x.empty? ? n : x
end

def map_upto(max, f)
  (1..max).map { |n| f[n] }
end

def be_short(item)
  case item
  when 'Fizz', 'Buzz'; item.chr
  when Integer; 0
  else 'z'
  end
end

def fizzbuzz_string(max)
  map_upto(max, method(:fizzbuzz)).map { |item| be_short item }.join
end

def find_seq(*sequence)
  short_seq = sequence.map { |item| be_short item }
  str = fizzbuzz_string(100)
  min = Float::INFINITY
  pos = 0
  while pos = str.index(/#{short_seq.join('\d*')}/, pos)
    m = $&
    if m.size < min
      res = [*pos+1..pos+m.size]
      min = m.size
    end
    pos += 1
  end
  res
end

find_seq('Fizz') # => [3]
find_seq('Buzz') # => [5]
find_seq('Fizz', 'Buzz') # => [9, 10]
find_seq('Buzz', 'Fizz') # => [5, 6]
find_seq('Fizz', 'Buzz', 'Fizz') # => [3, 4, 5, 6]
find_seq('Fizz', 'Fizz') # => [6, 7, 8, 9]
find_seq('Fizz', 'Fizz', 'Buzz') # => [6, 7, 8, 9, 10]
find_seq('Buzz', 'Fizz', 'Buzz') # => nil