模範解答

lib/sg_romanizer.rb

@@ -1,9 +1,28 @@
 class SgRomanizer
+  TABLE = [
+    %w[I II III IV V VI VII VIII IX],
+    %w[X XX XXX XL L LX LXX LXXX XC],
+    %w[C CC CCC CD D DC DCC DCCC CM],
+    %w[M MM MMM],
+  ].freeze
+
   def romanize(arabic)
-    # write your code here
+    arabic.digits.filter_map.with_index do |digit, y_pos|
+      TABLE[y_pos][digit - 1] if digit.nonzero?
+    end.reverse.join
   end
 
   def deromanize(roman)
-    # write your code here
+    copied_roman = roman.dup
+    positions = []
+    TABLE.reverse.each_with_index do |nums, y_pos|
+      nums.reverse.each_with_index do |num, x_pos|
+        positions << [y_pos, x_pos] if copied_roman.delete_prefix!(num)
+      end
+    end
+    positions.sum do |y_pos, x_pos|
+      max_x_pos = y_pos.zero? ? 3 : 9
+      10**(TABLE.size - y_pos - 1) * (max_x_pos - x_pos)
+    end
   end
 end