Problem 89

089.rb

@@ -0,0 +1,120 @@
+require 'pp'
+
+roman_numerals = []
+file = IO.readlines('roman.txt')
+file.each do |roman_numeral|
+  roman_numerals << roman_numeral.strip
+end
+
+$numerals = {
+  'M' => 1000,
+  'D' => 500,
+  'C' => 100,
+  'L' => 50,
+  'X' => 10,
+  'V' => 5,
+  'I' => 1
+}
+
+$choices = [
+  {
+    value: 1000,
+    numeral: 'M',
+    subtractive: false
+  },
+  {
+    value: 900,
+    numeral: 'CM',
+    subtractive: true,
+    replacement: 'DCCCC'
+  },
+  {
+    value: 500,
+    numeral: 'D',
+    subtractive: false
+  },
+  {
+    value: 400,
+    numeral: 'CD',
+    subtractive: true,
+    replacement: 'CCCC'
+  },
+  {
+    value: 100,
+    numeral: 'C',
+    subtractive: false
+  },
+  {
+    value: 90,
+    numeral: 'XC',
+    subtractive: true,
+    replacement: 'LXXXX'
+  },
+  {
+    value: 50,
+    numeral: 'L',
+    subtractive: false
+  },
+  {
+    value: 40,
+    numeral: 'XL',
+    subtractive: true,
+    replacement: 'XXXX'
+  },
+  {
+    value: 10,
+    numeral: 'X',
+    subtractive: false
+  },
+  {
+    value: 9,
+    numeral: 'IX',
+    subtractive: true,
+    replacement: 'VIIII'
+  },
+  {
+    value: 5,
+    numeral: 'V',
+    subtractive: false
+  },
+  {
+    value: 4,
+    numeral: 'IV',
+    subtractive: true,
+    replacement: 'IIII'
+  },
+  {
+    value: 1,
+    numeral: 'I',
+    subtractive: false
+  }
+]
+
+$subtractives = $choices.select{|c| c[:subtractive]}
+
+def build_roman_numeral(decimal_representation)
+  roman_numeral = ''
+  while decimal_representation > 0 do
+    next_numeral = $choices.find{|i| i[:value] <= decimal_representation}
+    decimal_representation -= next_numeral[:value]
+    roman_numeral += next_numeral[:numeral]
+  end
+  roman_numeral
+end
+
+def interpret_roman_numeral(roman_numeral)
+  roman_numeral = roman_numeral.dup
+  $subtractives.each do |s|
+    roman_numeral.gsub!(s[:numeral], s[:replacement])
+  end
+  roman_numeral.chars.reduce(0) { |sum, letter|
+    sum + $numerals[letter]
+  }
+end
+
+pp roman_numerals.inject(0) { |total, original_numeral|
+  decimal_representation = interpret_roman_numeral(original_numeral)
+  optimal_numeral = build_roman_numeral(decimal_representation)
+  diff = original_numeral.length - optimal_numeral.length
+  total + diff
+}