2019: Day 14 Part 1

2019/day14/part1.rb

@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+Chemical = Struct.new(:amount, :name) do
+  def pretty_print(pp)
+    pp.text to_s
+  end
+
+  def to_s
+    "#{amount} #{name}"
+  end
+end
+
+Formula = Struct.new(:product, :reactants) do
+  def produces?(name)
+    product.name == name
+  end
+
+  def pretty_print(pp)
+    pp.text to_s
+  end
+
+  def to_s
+    "#{product} <= #{reactants.join(', ')}"
+  end
+end
+
+def parse_chemical(text)
+  parts = text.split(' ')
+  amount = parts[0].to_i
+  name = parts[1].strip
+  Chemical.new(amount, name)
+end
+
+def parse(input)
+  input.lines.map do |line|
+    left, right = line.split('=>')
+
+    product = parse_chemical(right)
+    reactants = left.split(',').map { |text| parse_chemical(text) }
+    Formula.new(product, reactants)
+  end
+end
+
+input = File.read(File.join(__dir__, 'input'))
+formulas = parse(input)
+
+have = Hash.new { |hash, key| hash[key] = 0 }
+need = Hash.new { |hash, key| hash[key] = 0 }
+need['FUEL'] = 1
+ore = 0
+
+until need.empty?
+  product, amount = need.shift
+  next if amount.zero?
+
+  formula = formulas.find { |f| f.produces? product }
+
+  needed = (amount - have[product])
+
+  runs = (needed.fdiv formula.product.amount).ceil
+
+  formula.reactants.each do |r|
+    wanted = runs * r.amount
+    already_have = have[r.name]
+    can_use = [already_have, wanted].min
+    more = wanted - can_use
+
+    have[r.name] -= can_use
+    if r.name == 'ORE'
+      ore += more
+    else
+      need[r.name] += more
+    end
+  end
+
+  yielded = runs * formula.product.amount
+  extra = yielded - needed
+  have[product] += extra
+end
+puts ore