Add solution for 2015 day 19 part 1

2015/day-19/.ruby-version

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+3.0.0

2015/day-19/inputs/puzzle.txt

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+Al => ThF
+Al => ThRnFAr
+B => BCa
+B => TiB
+B => TiRnFAr
+Ca => CaCa
+Ca => PB
+Ca => PRnFAr
+Ca => SiRnFYFAr
+Ca => SiRnMgAr
+Ca => SiTh
+F => CaF
+F => PMg
+F => SiAl
+H => CRnAlAr
+H => CRnFYFYFAr
+H => CRnFYMgAr
+H => CRnMgYFAr
+H => HCa
+H => NRnFYFAr
+H => NRnMgAr
+H => NTh
+H => OB
+H => ORnFAr
+Mg => BF
+Mg => TiMg
+N => CRnFAr
+N => HSi
+O => CRnFYFAr
+O => CRnMgAr
+O => HP
+O => NRnFAr
+O => OTi
+P => CaP
+P => PTi
+P => SiRnFAr
+Si => CaSi
+Th => ThCa
+Ti => BP
+Ti => TiTi
+e => HF
+e => NAl
+e => OMg
+
+CRnCaSiRnBSiRnFArTiBPTiTiBFArPBCaSiThSiRnTiBPBPMgArCaSiRnTiMgArCaSiThCaSiRnFArRnSiRnFArTiTiBFArCaCaSiRnSiThCaCaSiRnMgArFYSiRnFYCaFArSiThCaSiThPBPTiMgArCaPRnSiAlArPBCaCaSiRnFYSiThCaRnFArArCaCaSiRnPBSiRnFArMgYCaCaCaCaSiThCaCaSiAlArCaCaSiRnPBSiAlArBCaCaCaCaSiThCaPBSiThPBPBCaSiRnFYFArSiThCaSiRnFArBCaCaSiRnFYFArSiThCaPBSiThCaSiRnPMgArRnFArPTiBCaPRnFArCaCaCaCaSiRnCaCaSiRnFYFArFArBCaSiThFArThSiThSiRnTiRnPMgArFArCaSiThCaPBCaSiRnBFArCaCaPRnCaCaPMgArSiRnFYFArCaSiThRnPBPMgAr

2015/day-19/inputs/test.txt

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+H => HO
+H => OH
+O => HH
+
+HOH

2015/day-19/main.rb

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+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "pathname"
+require "set"
+
+def uppercase?(char)
+  char.ord.between?(65, 90)
+end
+
+def parse_file(file)
+  rules = []
+  input = nil
+
+  rules_parsed = false
+  file.each_line do |line|
+    line = line.chomp
+    if line.empty?
+      rules_parsed = true
+    elsif rules_parsed
+      input = line.each_char.slice_before { |x| uppercase?(x) }.map(&:join)
+    else
+      line.split(" => ") => [lhs, rhs]
+      replacement = rhs.each_char.slice_before { |x| uppercase?(x) }.map(&:join)
+      rules.push([lhs, replacement])
+    end
+  end
+
+  [input, rules]
+end
+
+def apply_rules(input, rules)
+  molecules = Set.new
+
+  input.each_with_index do |item, idx|
+    rules.select { |(x, _)| x == item }.each do |(_, re)|
+      head = input[...idx].join
+      tail = input[(idx+1)..].join
+
+      molecules.add("#{head}#{re.join}#{tail}")
+    end
+  end
+
+  molecules
+end
+
+def main(file_paths)
+  file_paths.each do |file_path|
+    puts "File: #{file_path}"
+    input, rules = parse_file(file_path)
+
+    solution1 = apply_rules(input, rules).size
+    puts "  Solution 1: #{solution1}"
+  end
+end
+
+main(ARGV.map { |x| Pathname(x) })