Refactored to_roman to use substraction strategy

invadersmustdie · Dec 26, 2011 · d315e02 · d315e02
1 parent e1c721f
commit d315e02
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Showing 2 changed files with 33 additions and 13 deletions.
diff --git a/lib/arrabiata.rb b/lib/arrabiata.rb
@@ -4,13 +4,19 @@ class NoZeroInRomanNumbers < ArrabiataError; end
   class UnknownRomanNumberError < ArrabiataError; end
 
   CONVERSION = {
-    "M" => 1000,
-    "D" => 500,
-    "C" => 100,
-    "L" => 50,
-    "X" => 10,
-    "V" => 5,
-    "I" => 1
+    "M"     => 1000,
+    "CM"    => 900,
+    "D"     => 500,
+    "CD"    => 400,
+    "C"     => 100,
+    "XC"    => 90,
+    "L"     => 50,
+    "XL"    => 40,
+    "X"     => 10,
+    "IX"    => 9,
+    "V"     => 5,
+    "IV"    => 4,
+    "I"     => 1
   }
 
   def self.to_roman(n)
@@ -19,12 +25,10 @@ def self.to_roman(n)
 
     result = ""
 
-    # NOTE: this version doesn't yet respects the subtractive principle
-    CONVERSION.sort_by { |d| d.last }.reverse.each do |k|
-      x = n / k.last
-      if x != 0
-        result << k.first * x
-        n = n - x * k.last
+    CONVERSION.sort_by { |d| d.last }.reverse.each do |roman, arabic|
+      while(n >= arabic) do
+        result << roman
+        n -= arabic
       end
     end
 

diff --git a/spec/arrabiata_to_roman_spec.rb b/spec/arrabiata_to_roman_spec.rb
@@ -32,4 +32,20 @@
   it "should convert 2855 to MMDCCCLV" do
     Arrabiata.to_roman(2855).should == "MMDCCCLV"
   end
+
+  it "should convert 79 to LXXIX" do
+    Arrabiata.to_roman(79).should == "LXXIX"
+  end
+
+  it "should convert 4 to IV" do
+    Arrabiata.to_roman(4).should == "IV"
+  end
+
+  it "should convert 19 to XIX" do
+    Arrabiata.to_roman(19).should == "XIX"
+  end
+
+  it "should convert 8759 to MMMMMMMMDCCLIX" do
+    Arrabiata.to_roman(8759).should == "MMMMMMMMDCCLIX"
+  end
 end