Year 2015 Day 19

Author: maneatingape

README.md

@@ -228,3 +228,4 @@ The minimal SBT project provides:
 | 16 | [Aunt Sue](https://adventofcode.com/2015/day/16) | [Source](src/main/scala/AdventOfCode2015/Day16.scala) |
 | 17 | [No Such Thing as Too Much](https://adventofcode.com/2015/day/17) | [Source](src/main/scala/AdventOfCode2015/Day17.scala) |
 | 18 | [Like a GIF For Your Yard](https://adventofcode.com/2015/day/18) | [Source](src/main/scala/AdventOfCode2015/Day18.scala) |
+| 19 | [Medicine for Rudolph](https://adventofcode.com/2015/day/19) | [Source](src/main/scala/AdventOfCode2015/Day19.scala) |

src/main/resources/AdventOfCode2015/Day19.txt

@@ -0,0 +1,45 @@
+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
+
+ORnPBPMgArCaCaCaSiThCaCaSiThCaCaPBSiRnFArRnFArCaCaSiThCaCaSiThCaCaCaCaCaCaSiRnFYFArSiRnMgArCaSiRnPTiTiBFYPBFArSiRnCaSiRnTiRnFArSiAlArPTiBPTiRnCaSiAlArCaPTiTiBPMgYFArPTiRnFArSiRnCaCaFArRnCaFArCaSiRnSiRnMgArFYCaSiRnMgArCaCaSiThPRnFArPBCaSiRnMgArCaCaSiThCaSiRnTiMgArFArSiThSiThCaCaSiRnMgArCaCaSiRnFArTiBPTiRnCaSiAlArCaPTiRnFArPBPBCaCaSiThCaPBSiThPRnFArSiThCaSiThCaSiThCaPTiBSiRnFYFArCaCaPRnFArPBCaCaPBSiRnTiRnFArCaPRnFArSiRnCaCaCaSiThCaRnCaFArYCaSiRnFArBCaCaCaSiThFArPBFArCaSiRnFArRnCaCaCaFArSiRnFArTiRnPMgArF

src/main/scala/AdventOfCode2015/Day19.scala

@@ -0,0 +1,51 @@
+package AdventOfCode2015
+
+object Day19:
+  type Rules = Set[(scala.util.matching.Regex, Seq[String])]
+
+  def parse(input: Seq[String]): (Seq[(String, String)], String) =
+    val index = input.indexOf("")
+    val pairs = input.take(index).map(_.split(" => ")).map(a => a(0) -> a(1))
+    (pairs, input(index + 1))
+
+  def makeRules(pairs: Seq[(String, String)]): Rules =
+    pairs.map((k,v) => (k.r, v)).groupMap(_._1)(_._2).toSet
+
+  def candidates(rules: Rules, input: String): Set[String] = rules.flatMap { case (key, values) =>
+    key.findAllMatchIn(input).flatMap(mat => values.map(input.patch(mat.start, _, mat.end - mat.start)))
+  }
+
+  def aStar(rules: Rules, start: String): Int =
+    val cost = collection.mutable.Map(start -> 0)
+    val todo = collection.mutable.PriorityQueue(start -> 0)(Ordering.by(-_._2))
+
+    while todo.nonEmpty do
+      val (current, _) = todo.dequeue()
+      if current == "e" then return cost(current)
+      val nextCost = cost(current) + 1
+
+      candidates(rules, current).foreach { next =>
+        if !cost.contains(next) || nextCost < cost(next) then
+          cost(next) = nextCost
+          val priority = nextCost + next.size
+          todo.enqueue(next -> priority)
+      }
+    end while
+
+    -1
+  end aStar
+
+  def part1(input: Seq[String]): Int =
+    val (pairs, start) = parse(input)
+    val rules = makeRules(pairs)
+    candidates(rules, start).size
+
+  def part2(input: Seq[String]): Int =
+    val (pairs, start) = parse(input)
+    val rules = makeRules(pairs.map(_.swap))
+    aStar(rules, start)
+
+  def main(args: Array[String]): Unit =
+    val data = io.Source.fromResource("AdventOfCode2015/Day19.txt").getLines().toSeq
+    println(part1(data))
+    println(part2(data))

src/test/scala/AdventOfCode2015/Day19Suite.scala

@@ -0,0 +1,28 @@
+package AdventOfCode2015
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Day19Suite extends AnyFunSuite:
+  val sample1 = Seq(
+    "H => HO",
+    "H => OH",
+    "O => HH",
+    "",
+    "HOH")
+
+  test("Part 1 should handle sample input correctly") {
+    assert(Day19.part1(sample1) == 4)
+  }
+
+  val sample2 = Seq(
+    "e => H",
+    "e => O",
+    "H => HO",
+    "H => OH",
+    "O => HH",
+    "",
+    "HOHOHO")
+
+  test("Part 2 should handle sample input correctly") {
+    assert(Day19.part2(sample2) == 6)
+  }