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1.1 Add specs for converting 1, 2, 3

  • spec/decimal_to_roman_spec.rb

    +require_relative "../converter"
+
+RSpec.describe Converter do
+  subject(:converter) { Converter.new }
+
+  def decimal_to_roman(decimal)
+    converter.decimal_to_roman(decimal)
+  end
+
+  it { expect(decimal_to_roman(1)).to eq "I"   }
+  it { expect(decimal_to_roman(2)).to eq "II"  }
+  it { expect(decimal_to_roman(3)).to eq "III" }
+end
1.2 Make it pass

  • converter.rb

     class Converter
   def decimal_to_roman(decimal)
-    raise "NotImplementedError"
+    "I" * decimal
   end

   def roman_to_decimal(roman)
1.3 Add spec for convert 5 to V

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(1)).to eq "I"   }
   it { expect(decimal_to_roman(2)).to eq "II"  }
   it { expect(decimal_to_roman(3)).to eq "III" }
+
+  it { expect(decimal_to_roman(5)).to eq "V"   }
 end
1.4 Make it pass

  • converter.rb

     class Converter
   def decimal_to_roman(decimal)
-    "I" * decimal
+    if decimal == 5
+      "V"
+    else
+      "I" * decimal
+    end
   end

   def roman_to_decimal(roman)
1.5 Add spec for convert 6 to VI

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(3)).to eq "III" }

   it { expect(decimal_to_roman(5)).to eq "V"   }
+  it { expect(decimal_to_roman(6)).to eq "VI"  }
 end
1.6 Make it pass

  • converter.rb

     class Converter
   def decimal_to_roman(decimal)
-    if decimal == 5
-      "V"
-    else
-      "I" * decimal
+    n, result = decimal, ""
+
+    if n >= 5
+      result << "V"
+      n -= 5
     end
+
+    result << "I" * n
   end

   def roman_to_decimal(roman)
1.7 Add spec for convert 10 to X

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(5)).to eq "V"   }
   it { expect(decimal_to_roman(6)).to eq "VI"  }
+
+  it { expect(decimal_to_roman(10)).to eq "X"  }
 end
1.8 Make it pass

  • converter.rb

       def decimal_to_roman(decimal)
     n, result = decimal, ""

+    if n >= 10
+      result << "X"
+      n -= 10
+    end
+
     if n >= 5
       result << "V"
       n -= 5
1.9 Add spec for convert 20 to XX

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(6)).to eq "VI"  }

   it { expect(decimal_to_roman(10)).to eq "X"  }
+
+  it { expect(decimal_to_roman(20)).to eq "XX" }
 end
1.10 Make it pass

  • converter.rb

       def decimal_to_roman(decimal)
     n, result = decimal, ""

-    if n >= 10
+    while n >= 10
       result << "X"
       n -= 10
     end
1.11 Add spec for convert 4 to IV

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(2)).to eq "II"  }
   it { expect(decimal_to_roman(3)).to eq "III" }

+  it { expect(decimal_to_roman(4)).to eq "IV"  }
   it { expect(decimal_to_roman(5)).to eq "V"   }
   it { expect(decimal_to_roman(6)).to eq "VI"  }
1.12 Make it pass

  • converter.rb

           n -= 5
     end

+    if n >= 4
+      result << "IV"
+      n -= 4
+    end
+
     result << "I" * n
   end
1.13 Refactor a little bit

  • converter.rb

           n -= 4
     end

-    result << "I" * n
+    while n >= 1
+      result << "I"
+      n -= 1
+    end
+
+    result
   end

   def roman_to_decimal(roman)
1.14 All while works

  • converter.rb

           n -= 10
     end

-    if n >= 5
+    while n >= 5
       result << "V"
       n -= 5
     end

-    if n >= 4
+    while n >= 4
       result << "IV"
       n -= 4
     end
1.15 Don't Repeat Yourself

  • converter.rb

     class Converter
+  DECIMAL_ROMAN = [
+    [10, "X"],
+    [5,  "V"],
+    [4, "IV"],
+    [1,  "I"],
+  ]
+
   def decimal_to_roman(decimal)
     n, result = decimal, ""

-    while n >= 10
-      result << "X"
-      n -= 10
-    end
-
-    while n >= 5
-      result << "V"
-      n -= 5
-    end
-
-    while n >= 4
-      result << "IV"
-      n -= 4
-    end
-
-    while n >= 1
-      result << "I"
-      n -= 1
+    DECIMAL_ROMAN.each do |value, roman|
+      while n >= value
+        result << roman
+        n -= value
+      end
     end

     result
1.16 Add a spec for convert 9 to IX

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(5)).to eq "V"   }
   it { expect(decimal_to_roman(6)).to eq "VI"  }

+  it { expect(decimal_to_roman(9)).to eq "IX"  }
   it { expect(decimal_to_roman(10)).to eq "X"  }

   it { expect(decimal_to_roman(20)).to eq "XX" }
1.17 Make it pass

  • converter.rb

     class Converter
   DECIMAL_ROMAN = [
     [10, "X"],
+
+    [9, "IX"],
     [5,  "V"],
     [4, "IV"],
     [1,  "I"],
1.18 Add spec for convert 40, 50, 90

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(10)).to eq "X"  }

   it { expect(decimal_to_roman(20)).to eq "XX" }
+
+  it { expect(decimal_to_roman(40)).to eq "XL" }
+  it { expect(decimal_to_roman(50)).to eq "L"  }
+  it { expect(decimal_to_roman(90)).to eq "XC" }
 end
1.19 Make it pass

  • converter.rb

     class Converter
   DECIMAL_ROMAN = [
-    [10, "X"],
+    [90, "XC"],
+    [50,  "L"],
+    [40, "XL"],
+    [10,  "X"],

-    [9, "IX"],
-    [5,  "V"],
-    [4, "IV"],
-    [1,  "I"],
+    [9,  "IX"],
+    [5,   "V"],
+    [4,  "IV"],
+    [1,   "I"],
   ]

   def decimal_to_roman(decimal)
1.20 Add specs for convert 100, 400, 500, 900

  • spec/decimal_to_roman_spec.rb

         converter.decimal_to_roman(decimal)
   end

-  it { expect(decimal_to_roman(1)).to eq "I"   }
-  it { expect(decimal_to_roman(2)).to eq "II"  }
-  it { expect(decimal_to_roman(3)).to eq "III" }
+  it { expect(decimal_to_roman(1)).to eq "I"    }
+  it { expect(decimal_to_roman(2)).to eq "II"   }
+  it { expect(decimal_to_roman(3)).to eq "III"  }

-  it { expect(decimal_to_roman(4)).to eq "IV"  }
-  it { expect(decimal_to_roman(5)).to eq "V"   }
-  it { expect(decimal_to_roman(6)).to eq "VI"  }
+  it { expect(decimal_to_roman(4)).to eq "IV"   }
+  it { expect(decimal_to_roman(5)).to eq "V"    }
+  it { expect(decimal_to_roman(6)).to eq "VI"   }

-  it { expect(decimal_to_roman(9)).to eq "IX"  }
-  it { expect(decimal_to_roman(10)).to eq "X"  }
+  it { expect(decimal_to_roman(9)).to eq "IX"   }
+  it { expect(decimal_to_roman(10)).to eq "X"   }

-  it { expect(decimal_to_roman(20)).to eq "XX" }
+  it { expect(decimal_to_roman(20)).to eq "XX"  }

-  it { expect(decimal_to_roman(40)).to eq "XL" }
-  it { expect(decimal_to_roman(50)).to eq "L"  }
-  it { expect(decimal_to_roman(90)).to eq "XC" }
+  it { expect(decimal_to_roman(40)).to eq "XL"  }
+  it { expect(decimal_to_roman(50)).to eq "L"   }
+  it { expect(decimal_to_roman(90)).to eq "XC"  }
+
+  it { expect(decimal_to_roman(100)).to eq "C"  }
+  it { expect(decimal_to_roman(400)).to eq "CD" }
+  it { expect(decimal_to_roman(500)).to eq "D"  }
+  it { expect(decimal_to_roman(900)).to eq "CM" }
 end
1.21 Make it pass

  • converter.rb

     class Converter
   DECIMAL_ROMAN = [
-    [90, "XC"],
-    [50,  "L"],
-    [40, "XL"],
-    [10,  "X"],
+    [900, "CM"],
+    [500,  "D"],
+    [400, "CD"],
+    [100,  "C"],

-    [9,  "IX"],
-    [5,   "V"],
-    [4,  "IV"],
-    [1,   "I"],
+    [90,  "XC"],
+    [50,   "L"],
+    [40,  "XL"],
+    [10,   "X"],
+
+    [9,   "IX"],
+    [5,    "V"],
+    [4,   "IV"],
+    [1,    "I"],
   ]

   def decimal_to_roman(decimal)
1.22 Add spec for convert 1000

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(400)).to eq "CD" }
   it { expect(decimal_to_roman(500)).to eq "D"  }
   it { expect(decimal_to_roman(900)).to eq "CM" }
+
+  it { expect(decimal_to_roman(1000)).to eq "M" }
 end
1.23 Make it pass

  • converter.rb

     class Converter
   DECIMAL_ROMAN = [
+    [1000, "M"],
+
     [900, "CM"],
     [500,  "D"],
     [400, "CD"],
1.24 Make our specs complete

  • spec/decimal_to_roman_spec.rb

       it { expect(decimal_to_roman(900)).to eq "CM" }

   it { expect(decimal_to_roman(1000)).to eq "M" }
+
+  it "339 to CCCXXXIX" do
+    expect(decimal_to_roman(339)).to eq "CCCXXXIX"
+  end
+
+  it "1987 to MCMLXXXVII" do
+    expect(decimal_to_roman(1987)).to eq "MCMLXXXVII"
+  end
+
+  it "1999 to MCMXCIX" do
+    expect(decimal_to_roman(1999)).to eq "MCMXCIX"
+  end
 end
2.1 Add specs for elements of roman

  • spec/roman_to_decimal_spec.rb

    +require_relative "../converter"
+
+RSpec.describe Converter do
+  subject(:converter) { Converter.new }
+
+  def roman_to_decimal(roman)
+    converter.roman_to_decimal(roman)
+  end
+
+  it { expect(roman_to_decimal("I")).to eq 1    }
+
+  it { expect(roman_to_decimal("IV")).to eq 4   }
+  it { expect(roman_to_decimal("V")).to eq 5    }
+  it { expect(roman_to_decimal("IX")).to eq 9   }
+  it { expect(roman_to_decimal("X")).to eq 10   }
+
+  it { expect(roman_to_decimal("XL")).to eq 40  }
+  it { expect(roman_to_decimal("L")).to eq 50   }
+  it { expect(roman_to_decimal("XC")).to eq 90  }
+
+  it { expect(roman_to_decimal("C")).to eq 100  }
+  it { expect(roman_to_decimal("CD")).to eq 400 }
+  it { expect(roman_to_decimal("D")).to eq 500  }
+  it { expect(roman_to_decimal("CM")).to eq 900 }
+
+  it { expect(roman_to_decimal("M")).to eq 1000 }
+end
2.2 Make it pass

  • converter.rb

         raise "NotImplementedError"
   end

+  ROMAN_VALUES = {
+    "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 roman_to_decimal(roman)
-    raise "NotImplementedError"
+    ROMAN_VALUES.fetch(roman) { 0 }
   end
 end
2.3 Add cases to make it fail

  • spec/roman_to_decimal_spec.rb

       it { expect(roman_to_decimal("CM")).to eq 900 }

   it { expect(roman_to_decimal("M")).to eq 1000 }
+
+  it "CCCXXXIX to 339" do
+    expect(roman_to_decimal("CCCXXXIX")).to eq 339
+  end
+
+  it "MCMLXXXVII to 1987" do
+    expect(roman_to_decimal("MCMLXXXVII")).to eq 1987
+  end
+
+  it "MCMXCIX to 1999" do
+    expect(roman_to_decimal("MCMXCIX")).to eq 1999
+  end
 end
2.4 Make it pass

  • converter.rb

       }

   def roman_to_decimal(roman)
+    result = 0
+    romans = roman.split("")
+
+    while !romans.empty?
+      first, second = romans
+
+      if value_of(first) >= value_of(second)
+        result += value_of(first)
+      else
+        result += value_of(second) - value_of(first)
+        romans.shift
+      end
+
+      romans.shift
+    end
+
+    result
+  end
+
+  def value_of(roman)
     ROMAN_VALUES.fetch(roman) { 0 }
   end
 end