Day 17

aoc/src/dev/ctsk/aoc/Main.scala

@@ -18,7 +18,8 @@ val solvers = Map[Int, Solver](
   13 -> Day13,
   14 -> Day14,
   15 -> Day15,
-  16 -> Day16
+  16 -> Day16,
+  17 -> Day17
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/days/Day17.scala

@@ -0,0 +1,78 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc.*
+
+import scala.util.boundary
+import scala.util.boundary.break
+
+object Day17 extends Solver(17):
+  case class Machine(var code: IndexedSeq[Long]):
+    def execute(
+        registers: Map[Char, Long],
+        output: Option[Int] = None
+    ): Vector[Long] =
+      val reg = Array.from(registers).sorted.map(_._2)
+      var pc = 0
+
+      def combo(i: Long): Long =
+        i match
+          case i if i <= 3          => i
+          case i if i > 3 && i <= 6 => reg(i.toInt - 4)
+
+      var out = Vector.empty[Long]
+      boundary:
+        while pc < code.length do
+          code(pc) match
+            case 0 => reg(0) >>= combo(code(pc + 1)); pc += 2
+            case 1 => reg(1) ^= code(pc + 1); pc += 2
+            case 2 => reg(1) = combo(code(pc + 1)) % 8; pc += 2
+            case 3 => if reg(0) != 0 then pc = code(pc + 1).toInt else pc += 2
+            case 4 => reg(1) = reg(1) ^ reg(2); pc += 2
+            case 5 =>
+              out :+= combo(code(pc + 1)) % 8;
+              if output.exists(_ >= out.length) then break()
+              pc += 2
+            case 6 => reg(1) = reg(0) >> combo(code(pc + 1)); pc += 2
+            case 7 => reg(2) = reg(0) >> combo(code(pc + 1)); pc += 2
+
+      out
+
+  def part1(machine: Machine, initialRegs: Map[Char, Long]): String =
+    machine.execute(initialRegs).mkString(",")
+
+  def part2(machine: Machine, initialRegs: Map[Char, Long]): Long =
+    val target = machine.code.reverse
+
+    def rec(pos: Int = 0, acc: Long = 0): Option[Long] =
+      if pos >= target.length then return Some(acc)
+      def check(aVal: Long): Boolean =
+        machine.execute(initialRegs.updated('A', aVal), Some(1)).head == target(
+          pos
+        )
+
+      (0 until 8)
+        .map((acc << 3) + _)
+        .filter(check)
+        .flatMap(rec(pos + 1, _))
+        .headOption
+
+    rec().get
+
+  override def run(input: os.ReadablePath): (Timings, Solution) =
+    val Array(initial_, code_) = os.read(input).split("\n\n")
+    val initialRegs = initial_.linesIterator
+      .map(line => {
+        val spl = line.split(" ");
+        (spl(1)(0) -> spl(2).toLong)
+      })
+      .toMap
+    val code = longs(code_)
+    val machine = Machine(code)
+
+    val (p1_time, p1_solution) = timed { part1(machine, initialRegs) }
+    val (p2_time, p2_solution) = timed { part2(machine, initialRegs) }
+
+    (
+      Timings(0, p1_time, p2_time),
+      Solution(p1_solution, Long.box(p2_solution))
+    )

data/17.ans

@@ -0,0 +1,2 @@
+2,0,7,3,0,3,1,3,7
+247839539763386

data/17.in

@@ -0,0 +1,5 @@
+Register A: 18427963
+Register B: 0
+Register C: 0
+
+Program: 2,4,1,1,7,5,0,3,4,3,1,6,5,5,3,0