diff --git a/lib/sg_romanizer.rb b/lib/sg_romanizer.rb
index 9ab2218..2bf6a09 100644
--- a/lib/sg_romanizer.rb
+++ b/lib/sg_romanizer.rb
@@ -1,9 +1,52 @@
 class SgRomanizer
+
+  BASE_SYMBOL={
+    1 => 'I',
+    5 => 'V',
+    10 => 'X',
+    50 => 'L',
+    100 => 'C',
+    500 => 'D',
+    1000 => 'M'
+  }
+
   def romanize(arabic)
-    # write your code here
+    result=''
+    splitted_arabic_arr=split_by_digits(arabic)
+    splitted_arabic_arr.each do |arabic|
+      msd = arabic.digits[-1]
+      # 最上位桁の値で場合わけ
+      result += case msd
+      when 1,5
+        BASE_SYMBOL[arabic]
+      when 2,3
+        BASE_SYMBOL[arabic/msd]*msd
+      when 4,9
+        BASE_SYMBOL[arabic/msd] + BASE_SYMBOL[arabic+arabic/msd] 
+      when 6,7,8
+        BASE_SYMBOL[arabic*5/msd] + BASE_SYMBOL[arabic/msd]*(msd-5)
+      end 
+    end
+    result
   end
 
   def deromanize(roman)
-    # write your code here
+    result = []
+    arabic_arr = roman.chars.map {|r| BASE_SYMBOL.key(r)}
+    arabic_arr.each.with_index do |arabic,idx|
+      next_arabic = idx == arabic_arr.size - 1 ? 0 : arabic_arr[idx+1]
+      if arabic < next_arabic
+        result.push(-arabic)
+      else
+        result.push(arabic)
+      end
+    end
+    result.sum
+  end
+
+  # 数字を桁ごとに分割する．例1） 1030 -> [1000,30]. 例2) 691 -> [600,90,1]
+  def split_by_digits(arabic)
+    digits_arr = arabic.digits
+    digits_arr.map.with_index {|n,idx| n*(10**idx)}.reverse.reject{|n| n==0}
   end
 end