Day 10 cleanup

aoc/src/Day10.scala

@@ -6,44 +6,25 @@ object Day10 extends App:
     .fromURL(getClass.getResource("day10Input.txt"))
     .mkString
     .split('\n')
-    .toList
-    .map(_.split(" ")).map {
-      case Array(inst, value) => (inst, value.toInt)
-      case Array(inst)        => (inst, 0)
-    }
+    .map(_.split(" "))
     .flatMap {
-      case inst @ ("noop", _) => List(inst)
-      case inst @ ("addx", _) => List(("noop", 0), inst)
+      case Array("addx", value) => List(0, value.toInt)
+      case Array("noop")        => List(0)
     }
 
-  val execution = input.scanLeft((1, 1)) {
-    case ((register, cycle), ("noop", _))     => (register, cycle + 1)
-    case ((register, cycle), ("addx", value)) => (register + value, cycle + 1)
-    case ((register, cycle), _)               => (register, cycle + 1)
-  }
+  val registerStates = input.scan(1)(_ + _)
 
-  val interestingSignals =
-    (20 to execution.last._2).filter(cycle => cycle == 20 || (cycle + 20) % 40 == 0)
-
-  val part1 = execution
-    .filter(state => interestingSignals.contains(state._2))
-    .map(_._1)
-    .zip(interestingSignals)
-    .map(_ * _)
-    .sum
+  val part1 = (20 to 220 by 40).map(s => registerStates(s - 1) * s).sum
   println(s"Part 1: $part1")
 
-  def renderRow(rowExecution: List[(Int, Int)]): String =
-    rowExecution.foldLeft("") { case (line, (register, cycle)) =>
-      val spritePosition = register - 1 to register + 1
-      if spritePosition.contains((cycle - 1) % 40) then line + "#"
-      else line + "."
-    }
-
-  val part2 = execution
+  val part2 = registerStates
     .grouped(40)
-    .map(renderRow)
+    .map(
+      _.zip(0 to 39)
+        .map((reg, cycle) => Math.abs(reg - cycle) <= 1)
+        .map(if _ then "#" else ".")
+        .mkString
+    )
     .mkString("\n")
-  println(s"Part 2:")
+  println("Part 2:")
   println(part2)
-end Day10