Roman Numerals in Ruby: Converting Roman Numerals to Integers

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In this comprehensive guide, we explore the fascinating world of Roman numerals and how to translate them into integers using Ruby. From understanding the principles of Roman numerals to implementing a robust conversion function in Ruby, this article covers everything you need to know to master Roman numeral conversion in your Ruby projects.

Roman numerals are a numeric system that originated in ancient Rome and are still used today in various contexts. While they may seem archaic, understanding how to convert Roman numerals to integers is a valuable skill, especially for programmers working with historical data or specialized applications. In this article, we’ll dive deep into the process of converting Roman numerals to integers using the Ruby programming language.

Understanding Roman Numerals

Roman numerals are represented by seven symbols: I, V, X, L, C, D, and M, which correspond to the decimal values 1, 5, 10, 50, 100, 500, and 1000, respectively. The value of a Roman numeral is determined by adding or subtracting the values of its symbols according to certain rules:

  • Symbols are arranged from left to right in descending order of value.
  • If a symbol of smaller value precedes a symbol of larger value, the smaller value is subtracted from the larger value.
  • Otherwise, the values of the symbols are added together.

Writing a Roman to Integer Conversion Function in Ruby

Now that we understand the principles of Roman numerals, let’s implement a Ruby function to convert Roman numerals to integers:

def roman_to_integer(roman)
  roman_values = {
    'I' => 1,
    'V' => 5,
    'X' => 10,
    'L' => 50,
    'C' => 100,
    'D' => 500,
    'M' => 1000

  total = 0
  prev_value = 0

  roman.chars.reverse_each do |char|
    value = roman_values[char]

    if value < prev_value
      total -= value
      total += value

    prev_value = value


Testing the Roman to Integer Conversion Function

Let’s test our roman_to_integer function with some Roman numerals:

puts roman_to_integer('III') # Output: 3
puts roman_to_integer('IV')  # Output: 4
puts roman_to_integer('IX')  # Output: 9
puts roman_to_integer('LVIII') # Output: 58
puts roman_to_integer('MCMXCIV') # Output: 1994

Explaining the Implementation

  • We define a hash roman_values to map Roman numeral characters to their corresponding integer values.
  • We iterate over each character of the Roman numeral string in reverse order, calculating the integer value of each character.
  • If the current character’s value is less than the previous character’s value, we subtract it from the total; otherwise, we add it to the total.
  • Finally, we return the total value.
Author: user