Parse Int

parset_int.rb

NUMERALS_MAP = {
  'zero' => 0,
  'one' => 1,
  'two' => 2,
  'three' => 3,
  'four' => 4,
  'five' => 5,
  'six' => 6,
  'seven' => 7,
  'eight' => 8,
  'nine' => 9,
  'ten' => 10,
  'eleven' => 11,
  'twelve' => 12,
  'thirteen' => 13,
  'sixteen' => 16,
  'seventeen' => 17,
  'eighteen' => 18,
  'nineteen' => 19,
  'twenty' => 20,
  'thirty' => 30,
  'forty' => 40,
  'fifty' => 50,
  'sixty' => 60,
  'seventy' => 70,
  'eighty' => 80,
  'ninety' => 90,
  'hundred' => 100,
  'thousand' => 1000,
  'million' => 1000000
}

def parse_int(string)
  numerals = string.split(/[\s,-]/).reject { |n| n == 'and' }
  raise ArgumentError, 'Argument is not a numeral' unless numerals.all? { |n| NUMERALS_MAP.key? n }

  numbers = numerals.map { |n|  NUMERALS_MAP[n] }

  total = 0
  numbers.each_with_index do |number, index|
    next if number == 100

    if numbers[index + 1] == 100
      total += number * numbers[index + 1]
    elsif number == 1000
      total *= number
    else
      total += number
    end
  end

  total
end

puts parse_int('one') == 1
puts parse_int('twenty') == 20
puts parse_int('ninety-nine') == 99
puts parse_int('two hundred forty-six') == 246
puts parse_int('seven hundred eighty-three thousand nine hundred and nineteen') == 783919