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