Day 3

core/src/main/scala/tf/bug/aoc/Day.scala

@@ -5,5 +5,5 @@ import cats.effect._
 import fs2._
 
 trait Day:
-  def part1[F[_]: Sync]: Pipe[F, String, String]
+  def part1[F[_]: Async]: Pipe[F, String, String]
-  def part2[F[_]: Sync]: Pipe[F, String, String]
+  def part2[F[_]: Async]: Pipe[F, String, String]

core/src/main/scala/tf/bug/aoc/Main.scala

@@ -1,5 +1,6 @@
 package tf.bug.aoc
 
+import cats._
 import cats.effect._
 import cats.effect.std.Console
 import cats.syntax.all._
@@ -25,8 +26,8 @@ object Main extends IOApp:
         .compile.drain
     }.as(ExitCode.Success)
 
-  def selectYear[F[_]: Sync: Console]: F[Year] =
+  def selectYear[F[_]: Monad: Console]: F[Year] =
-    val ask = Sync[F].delay(print("Select year: "))
+    val ask = Console[F].print("Select year: ")
     val receive = Console[F].readLine
     val year: F[Option[Year]] = (ask >> receive).map(_.toIntOption >>= years.get)
     year.flatMap {
@@ -34,8 +35,8 @@ object Main extends IOApp:
       case None => selectYear[F]
     }
   
-  def selectDay[F[_]: Sync: Console](year: Year): F[Day] =
+  def selectDay[F[_]: Monad: Console](year: Year): F[Day] =
-    val ask = Sync[F].delay(print("Select day: "))
+    val ask = Console[F].print("Select day: ")
     val receive = Console[F].readLine
     val day: F[Option[Day]] = (ask >> receive).map(_.toIntOption >>= year.days.get)
     day.flatMap {
@@ -43,8 +44,8 @@ object Main extends IOApp:
       case None => selectDay[F](year)
     }
 
-  def selectPart[F[_]: Sync: Console](day: Day): F[Pipe[F, String, String]] =
+  def selectPart[F[_]: Async: Console](day: Day): F[Pipe[F, String, String]] =
-    val ask = Sync[F].delay(print("Select part: "))
+    val ask = Console[F].print("Select part: ")
     val receive = Console[F].readLine
     val part: F[Option[Int]] = (ask >> receive).map(_.toIntOption)
     part.flatMap {

core/src/main/scala/tf/bug/aoc/y2020/Day1.scala

@@ -10,10 +10,10 @@ import tf.bug.aoc.Day
 
 object Day1 extends Day:
 
-  override def part1[F[_]: Sync]: Pipe[F, String, String] =
+  override def part1[F[_]: Async]: Pipe[F, String, String] =
     parts[F](2)
 
-  override def part2[F[_]: Sync]: Pipe[F, String, String] =
+  override def part2[F[_]: Async]: Pipe[F, String, String] =
     parts[F](3)
 
   def parts[F[_]: Sync](nums: Int): Pipe[F, String, String] =

core/src/main/scala/tf/bug/aoc/y2020/Day2.scala

@@ -23,13 +23,13 @@ object Day2 extends Day:
         Entry(policy, password)
     }
 
-  override def part1[F[_]: Sync]: Pipe[F, String, String] =
+  override def part1[F[_]: Async]: Pipe[F, String, String] =
     parts[F] { ent =>
       val charCount = ent.password.count(_ == ent.policy.letter)
       ent.policy.min <= charCount && charCount <= ent.policy.max
     }
 
-  override def part2[F[_]: Sync]: Pipe[F, String, String] =
+  override def part2[F[_]: Async]: Pipe[F, String, String] =
     parts[F] { ent =>
       val a = ent.policy.min <= ent.password.length && ent.password.charAt(ent.policy.min - 1) == ent.policy.letter
       val b = ent.policy.max <= ent.password.length && ent.password.charAt(ent.policy.max - 1) == ent.policy.letter

core/src/main/scala/tf/bug/aoc/y2020/Day3.scala

@@ -0,0 +1,46 @@
+package tf.bug.aoc.y2020
+
+import cats.effect._
+import cats.syntax.all._
+import fs2._
+import tf.bug.aoc.Day
+
+object Day3 extends Day:
+
+  case class Path(x: Int, treeCount: Long)
+
+  override def part1[F[_]: Async]: Pipe[F, String, String] =
+    _.through(checkSlope[F](3, 1)).map(_.show)
+
+  override def part2[F[_]: Async]: Pipe[F, String, String] =
+    (lines: Stream[F, String]) => {
+      val pipes: Vector[Pipe[F, String, Long]] = Vector(
+        checkSlope[F](1, 1),
+        checkSlope[F](3, 1),
+        checkSlope[F](5, 1),
+        checkSlope[F](7, 1),
+        checkSlope[F](1, 2),
+      )
+      val broadcast: Stream[F, String] => Stream[F, Stream[F, String]] = concurrent.Broadcast[F, String](pipes.size)
+      val channels: Stream[F, Stream[F, String]] = lines.through(broadcast).take(pipes.size)
+      val results: Stream[F, Long] = channels.zipWithIndex.map {
+        case (channel, ind) =>
+          val pipe = pipes(ind.toInt)
+          channel.through(pipe)
+      }.parJoin(pipes.size)
+      results.fold(1L)(_ * _).map(_.show)
+    }
+
+  def checkSlope[F[_]](right: Int, down: Int): Pipe[F, String, Long] =
+    (lines: Stream[F, String]) => {
+      lines.chunkN(down, true).fold(Path(0, 0L)) {
+        case (Path(x, numTrees), group) =>
+          group.head match {
+            case Some(line) =>
+              val isTree = line.charAt(x % line.length) == '#'
+              Path(x + right, if(isTree) numTrees + 1L else numTrees)
+            case None =>
+              Path(x, numTrees)
+          }
+      }.map(_.treeCount)
+    }

core/src/main/scala/tf/bug/aoc/y2020/y2020.scala

@@ -6,4 +6,5 @@ object y2020 extends Year:
   override def days: Map[Int, Day] = Map(
     1 -> Day1,
     2 -> Day2,
+    3 -> Day3,
   )