Initial commit

.gitignore

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+
+# Created by https://www.toptal.com/developers/gitignore/api/sbt,scala,metals,bloop,visualstudiocode
+# Edit at https://www.toptal.com/developers/gitignore?templates=sbt,scala,metals,bloop,visualstudiocode
+
+### Bloop ###
+.bloop/
+
+### Metals ###
+.metals/
+project/metals.sbt
+project/project/
+
+### SBT ###
+# Simple Build Tool
+# http://www.scala-sbt.org/release/docs/Getting-Started/Directories.html#configuring-version-control
+
+dist/*
+target/
+lib_managed/
+src_managed/
+project/boot/
+project/plugins/project/
+.history
+.cache
+.lib/
+
+### Scala ###
+*.class
+*.log
+
+### VisualStudioCode ###
+.vscode/*
+!.vscode/tasks.json
+!.vscode/launch.json
+*.code-workspace
+
+### VisualStudioCode Patch ###
+# Ignore all local history of files
+.ionide
+
+# End of https://www.toptal.com/developers/gitignore/api/sbt,scala,metals,bloop,visualstudiocode

build.sbt

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+lazy val core = (project in file("core")).settings(
+  organization := "tf.bug",
+  name := "aoc",
+  version := "0.1.0",
+  scalaVersion := "3.0.0-M2",
+  libraryDependencies ++= Seq(
+    "org.typelevel" %% "cats-core" % "2.3.0",
+    "org.typelevel" %% "cats-effect" % "3.0.0-M4",
+    "co.fs2" %% "fs2-core" % "3.0.0-M6",
+    "co.fs2" %% "fs2-io" % "3.0.0-M6",
+  ),
+)

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

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+package tf.bug.aoc
+
+import cats._
+import cats.effect._
+import fs2._
+
+trait Day:
+  def part1[F[_]: Sync]: Pipe[F, String, String]
+  def part2[F[_]: Sync]: Pipe[F, String, String]

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

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+package tf.bug.aoc
+
+import cats.effect._
+import cats.effect.std.Console
+import cats.syntax.all._
+import java.nio.charset.StandardCharsets
+import fs2._
+
+object Main extends IOApp:
+
+  def years: Map[Int, Year] = Map(
+    2020 -> y2020.y2020,
+  )
+
+  override def run(args: List[String]): IO[ExitCode] =
+    val year: IO[Year] = selectYear[IO]
+    val day: IO[Day] = year >>= selectDay[IO]
+    val part: IO[Pipe[IO, String, String]] = day >>= selectPart[IO]
+    part.flatMap { p =>
+      io.stdinUtf8[IO](1024)
+        .through(text.lines)
+        .takeWhile(_.nonEmpty)
+        .through(p)
+        .through(io.stdoutLines(StandardCharsets.UTF_8))
+        .compile.drain
+    }.as(ExitCode.Success)
+
+  def selectYear[F[_]: Sync: Console]: F[Year] =
+    val ask = Sync[F].delay(print("Select year: "))
+    val receive = Console[F].readLine
+    val year: F[Option[Year]] = (ask >> receive).map(_.toIntOption >>= years.get)
+    year.flatMap {
+      case Some(year) => year.pure[F]
+      case None => selectYear[F]
+    }
+  
+  def selectDay[F[_]: Sync: Console](year: Year): F[Day] =
+    val ask = Sync[F].delay(print("Select day: "))
+    val receive = Console[F].readLine
+    val day: F[Option[Day]] = (ask >> receive).map(_.toIntOption >>= year.days.get)
+    day.flatMap {
+      case Some(day) => day.pure[F]
+      case None => selectDay[F](year)
+    }
+
+  def selectPart[F[_]: Sync: Console](day: Day): F[Pipe[F, String, String]] =
+    val ask = Sync[F].delay(print("Select part: "))
+    val receive = Console[F].readLine
+    val part: F[Option[Int]] = (ask >> receive).map(_.toIntOption)
+    part.flatMap {
+      case Some(1) => day.part1[F].pure[F]
+      case Some(2) => day.part2[F].pure[F]
+      case _ => selectPart[F](day)
+    }

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

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+package tf.bug.aoc
+
+trait Year:
+  def days: Map[Int, Day]

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

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+package tf.bug.aoc.y2020
+
+import cats._
+import cats.effect._
+import cats.syntax.all._
+import fs2._
+import java.nio.charset.StandardCharsets
+import scala.util.Try
+import tf.bug.aoc.Day
+
+object Day1 extends Day:
+
+  def part1[F[_]: Sync]: Pipe[F, String, String] =
+    parts[F](2)
+
+  def part2[F[_]: Sync]: Pipe[F, String, String] =
+    parts[F](3)
+
+  def parts[F[_]: Sync](nums: Int): Pipe[F, String, String] =
+    (lines: Stream[F, String]) => {
+      val ints: F[Vector[Int]] = lines
+        .map(_.toInt)
+        .compile.toVector
+      val result: F[Option[Int]] = ints.map(sumTargetProduct(2020, nums, _))
+      Stream.eval(result).map(_.show)
+    }
+  
+  def sumTargetProduct(target: Int, num: Int, ints: Vector[Int]): Option[Int] =
+    ints.combinations(num).collectFirst {
+      case v if v.sum == target => v.product
+    }

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

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+package tf.bug.aoc.y2020
+
+import tf.bug.aoc.{Day, Year}
+
+object y2020 extends Year:
+  override def days: Map[Int, Day] = Map(
+    1 -> Day1,
+  )

project/build.properties

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+sbt.version=1.4.4

project/plugins.sbt

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+addSbtPlugin("io.github.davidgregory084" % "sbt-tpolecat" % "0.1.16")
+addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.4.6")