Rosetta Code

Roman numerals/Decode

Convert a Roman numeral string back to its integer value.

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Sourcerosettacode/popular/roman_numerals_decode.vibe
def roman_value(char: string) -> int
  if char == "M"
    return 1000
  elsif char == "D"
    return 500
  elsif char == "C"
    return 100
  elsif char == "L"
    return 50
  elsif char == "X"
    return 10
  elsif char == "V"
    return 5
  elsif char == "I"
    return 1
  end
  0
end

def from_roman(roman: string) -> int
  roman_chars = roman.chars
  total = 0
  i = 0

  while i < roman.length
    current = roman_value(roman_chars.fetch(i))
    if i + 1 < roman.length
      next_val = roman_value(roman_chars.fetch(i + 1))
      if current < next_val
        total = total + (next_val - current)
        i = i + 2
      else
        total = total + current
        i = i + 1
      end
    else
      total = total + current
      i = i + 1
    end
  end

  total
end

def run -> { i: int, iv: int, mmxxiv: int, xcix: int, xlii: int }
  {
    i: from_roman("I"),
    iv: from_roman("IV"),
    xlii: from_roman("XLII"),
    xcix: from_roman("XCIX"),
    mmxxiv: from_roman("MMXXIV")
  }
end

Output

Click Run example to see the result.

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