implement romanize and deromanize

lib/sg_romanizer.rb

@@ -1,9 +1,63 @@
 class SgRomanizer
   def romanize(arabic)
-    # write your code here
+    raise ArgumentError unless (1..3999).cover?(arabic)
+
+    [1000, 100, 10, 1].map do |digit|
+      romasymbols = digit_to_romasymbols(digit)
+      adjusted_arabic = arabic % (digit * 10)
+      coefficient = (adjusted_arabic / digit).to_i
+      romanize_format(coefficient, romasymbols)
+    end.join
   end
 
   def deromanize(roman)
-    # write your code here
+    raise ArgumentError unless roman.match?(/^[MDCLXVI]+$/)
+
+    roman.split('').push('-').each_cons(2).map do |symbols|
+      num = romasymbol_to_num(symbols[0])
+      next_num = romasymbol_to_num(symbols[1])
+      num < next_num ? -num : num
+    end.sum
+  end
+
+  private
+
+  def digit_to_romasymbols(digit)
+    case digit
+    when 1000 then ['M', nil, nil]
+    when 100 then ['C', 'D', 'M']
+    when 10 then ['X', 'L', 'C']
+    when 1 then ['I', 'V', 'X']
+    else []
+    end
+  end
+
+  def romanize_format(num, symbols)
+    i,v,x = symbols
+    case num
+    when 1 then i
+    when 2 then i + i
+    when 3 then i + i + i
+    when 4 then i + v
+    when 5 then v
+    when 6 then v + i
+    when 7 then v + i + i
+    when 8 then v + i + i + i
+    when 9 then i + x
+    else ''
+    end
+  end
+
+  def romasymbol_to_num(symbol)
+    case symbol
+    when 'M' then 1000
+    when 'D' then 500
+    when 'C' then 100
+    when 'L' then 50
+    when 'X' then 10
+    when 'V' then 5
+    when 'I' then 1
+    else 0
+    end
   end
 end