Roman Numeral in Ruby

Published on 28 April 2022 (Updated: 02 February 2023)

Roman Numeral in Ruby

Welcome to the Roman Numeral in Ruby page! Here, you’ll find the source code for this program as well as a description of how the program works.

Current Solution

  "I": 1,
  "V": 5,
  "X": 10,
  "L": 50,
  "C": 100,
  "D": 500,
  "M": 1000

def roman_valid?(roman_numbers)
  return false if roman_numbers.any? { |roman_number| !ROMAN_VALUES.keys.include?(roman_number.to_sym) }  
  return false if roman_numbers.join.include?('MMMM')
  counter_numbers = roman_numbers.tally # Only on ruby 2.7+
  unless counter_numbers['M'].nil?
    return false if counter_numbers['M'] > 4
  counter_numbers.reject { |k| k == 'M' }.all? { |(_, counter)| counter <= 3 }

def roman_to_decimal(full_roman_number)
  return 'Usage: please provide a string of roman numerals' if full_roman_number.nil?
  return 0 if full_roman_number.empty?

  roman_numbers = full_roman_number.upcase.split('')
  return 'Error: invalid string of roman numerals' unless roman_valid?(roman_numbers)

  total = 0

  roman_numbers.each_with_index do |roman_number, index|
    current_value = ROMAN_VALUES[roman_number.to_sym]
    next_value = ROMAN_VALUES[roman_numbers[index+1]&.to_sym] || 0
    if (current_value >= next_value)
      total += current_value
      total -= current_value



Roman Numeral in Ruby was written by:

If you see anything you’d like to change or update, please consider contributing.

How to Implement the Solution

No ‘How to Implement the Solution’ section available. Please consider contributing.

How to Run the Solution

No ‘How to Run the Solution’ section available. Please consider contributing.