Day 16

aoc/src/Day16.scala

@@ -0,0 +1,76 @@
+import scala.io.Source
+import scala.util.chaining.*
+import scala.collection.mutable
+
+object Day16 extends App:
+
+  val valves = Source
+    .fromURL(getClass.getResource("day16Input.txt"))
+    .mkString
+    .split('\n')
+    .map(
+      _.drop(6)
+        .replaceAllLiterally("has flow rate=", "")
+        .replaceAllLiterally("; tunnels lead to valves", "")
+        .replaceAllLiterally("; tunnel leads to valve", "")
+        .replaceAllLiterally(",", "")
+        .split(" ")
+    )
+    .map(l => Valve(l.head, l(1).toInt, l.drop(2).toList))
+
+  final case class Valve(name: String, rate: Int, tunnels: List[String])
+
+  val valvesMap     = valves.map(v => (v.name, v)).toMap
+  val workingValves = valves.filter(_.rate > 0).map(_.name).toList
+
+  val distances = mutable.Map.from(
+    for
+      valve <- valves
+      targetValves = valves.map(_.name).map((_, 9999)).to(mutable.Map)
+    yield (valve.name, targetValves)
+  )
+
+  for
+    valve  <- valves
+    tunnel <- valve.tunnels
+  do distances(valve.name)(tunnel) = 1
+
+  for
+    k <- valves.map(_.name)
+    i <- valves.map(_.name)
+    j <- valves.map(_.name)
+    current = distances(i)(j)
+    dist    = distances(i)(k) + distances(k)(j)
+    if current > dist
+  do distances(i)(j) = dist
+
+  def computeFlow(current: String, rest: List[String], timeLeft: Int): Int =
+    rest
+      .filter(distances(current)(_) < timeLeft)
+      .map(r => (r, rest.filterNot(_ == r)))
+      .map { case (r, rest) =>
+        valvesMap(r).rate * (timeLeft - distances(current)(r) - 1) +
+          computeFlow(r, rest, timeLeft - distances(current)(r) - 1)
+      }
+      .prepended(0)
+      .max
+
+  def computeFlow2(current: String, rest: List[String], timeLeft: Int): Int =
+    rest
+      .filter(distances(current)(_) < timeLeft)
+      .map(r => (r, rest.filterNot(_ == r)))
+      .map { case (r, rest) =>
+        valvesMap(r).rate * (timeLeft - distances(current)(r) - 1) +
+          computeFlow2(r, rest, timeLeft - distances(current)(r) - 1)
+      }
+      .prepended(computeFlow("AA", rest, 26))
+      .max
+
+  val part1 = computeFlow("AA", workingValves, 30)
+  println("Part 1:")
+  println(part1)
+
+  val part2 = computeFlow2("AA", workingValves, 26)
+  println("Part 2:")
+  println(part2)
+end Day16