roman numerals

課題

アラビア数字(arabic numerals)を受け取って，ローマ数字(roman numerals)を返すmethodを書きなさい．

作成

ひとまず動くものを作ってみた．4桁の整数が入力されるものとして各桁を分割し，それぞれに対して4か9かそれ以外かという分岐を施した．

roman_numerals.rb

class Integer
    def arab_to_roman
    number = self
    m = number / 1000
    number = number % 1000
    c = number / 100
    number = number % 100
    x = number / 10
    number = number % 10
    i = number


    roman = 'M' * m
    if c == 9 
        roman += 'CM'
    elsif c == 4
        roman += 'CD'
    else
        roman += 'D' * (c / 5)
        c = c % 5
        roman += 'C' * c
    end
    if x == 9
        roman += 'XC'
    elsif x == 4
        roman += 'XL'
    else
        roman += 'L' * (x / 5)
        x = x % 5
        roman += 'X' * x
    end
    if i == 9
        roman += 'IX'
    elsif i == 4
        roman += 'IV'
    else
        roman += 'V' * (i / 5)
        i = i % 5
        roman += 'I' * i
    end
    puts roman
    end
end

[4, 15, 32, 44, 99, 439, 499, 961, 2254, 3782].each do |i|
    i.arab_to_roman
end

結果は，

IV
XV
XXXII
XLIV
XCIX
CDXXXIX
CDXCIX
CMLXI
MMCCLIV
MMMDCCLXXXII

動くけども冗長なコードになってダサい．

改造しよう．ifをcaseを用いて短縮することを考える．

roman_numerals.rb

class Integer
    def arab_to_roman
    number = self
    m = number / 1000
    number = number % 1000
    c = number / 100
    number = number % 100
    x = number / 10
    number = number % 10
    i = number


    roman = 'M' * m

    case c
    when 9 then roman += 'CM' #900
    when 4 then roman += 'CD' #400
    else
        roman += 'D' * (c / 5)
        c = c % 5
        roman += 'C' * c
    end

    case x
    when 9 then roman += 'XC' #90
    when 4 then roman += 'XL' #40
    else
        roman += 'L' * (x / 5)
        x = x % 5
        roman += 'X' * x
    end

    case i
    when 9 then roman += 'IX' #9
    when 4 then roman += 'IV' #4
    else
        roman += 'V' * (i / 5)
        i = i % 5
        roman += 'I' * i
    end

    puts roman
    end
end

[4, 15, 32, 44, 99, 439, 499, 961, 2254, 3782].each do |i|
    i.arab_to_roman
end

さらにcaseの動作は三回ともほぼ同じなので別のメソッドを作っておいて使用する．

roman_numerals.rb

class Integer
    def arab_to_roman
    number = self
    m = number / 1000
    number %= 1000
    c = number / 100
    number %= 100
    x = number / 10
    number %= 10
    i = number

    roman = 'M' * m

    roman = proc(roman, ["C","D","M"], c)
    roman = proc(roman, ["X","L","C"], x)
    roman = proc(roman, ["I","V","X"], i)

    puts roman
    end

    def proc(roman, sym, n)
    case n
    when 9 then roman += (sym[0]+sym[2])
    when 4 then roman += (sym[0]+sym[1])
    else
        roman += (sym[1] * (n / 5))
        n = n % 5
        roman += (sym[0] * n)
    end
    return roman
    end
end


[4, 15, 32, 44, 99, 439, 499, 961, 2254, 3782].each do |i|
    i.arab_to_roman
end

だいぶマシにはなった．まだ短くできるのかもしれないけども，僕はここまでしかできません．

まとめ

アラビア数字をローマ数字に変換するコードを作成した．

参考

---

• source ~/prog/github/grad_members_20f/members/miyanagi/post/roman.org