Day 11

aoc/resources/day11Input.txt

@@ -0,0 +1,55 @@
+Monkey 0:
+  Starting items: 61
+  Operation: new = old * 11
+  Test: divisible by 5
+    If true: throw to monkey 7
+    If false: throw to monkey 4
+
+Monkey 1:
+  Starting items: 76, 92, 53, 93, 79, 86, 81
+  Operation: new = old + 4
+  Test: divisible by 2
+    If true: throw to monkey 2
+    If false: throw to monkey 6
+
+Monkey 2:
+  Starting items: 91, 99
+  Operation: new = old * 19
+  Test: divisible by 13
+    If true: throw to monkey 5
+    If false: throw to monkey 0
+
+Monkey 3:
+  Starting items: 58, 67, 66
+  Operation: new = old * old
+  Test: divisible by 7
+    If true: throw to monkey 6
+    If false: throw to monkey 1
+
+Monkey 4:
+  Starting items: 94, 54, 62, 73
+  Operation: new = old + 1
+  Test: divisible by 19
+    If true: throw to monkey 3
+    If false: throw to monkey 7
+
+Monkey 5:
+  Starting items: 59, 95, 51, 58, 58
+  Operation: new = old + 3
+  Test: divisible by 11
+    If true: throw to monkey 0
+    If false: throw to monkey 4
+
+Monkey 6:
+  Starting items: 87, 69, 92, 56, 91, 93, 88, 73
+  Operation: new = old + 8
+  Test: divisible by 3
+    If true: throw to monkey 5
+    If false: throw to monkey 2
+
+Monkey 7:
+  Starting items: 71, 57, 86, 67, 96, 95
+  Operation: new = old + 7
+  Test: divisible by 17
+    If true: throw to monkey 3
+    If false: throw to monkey 1

aoc/src/Day11.scala

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+import scala.io.Source
+
+object Day11 extends App:
+
+  val input = Source
+    .fromURL(getClass.getResource("day11Input.txt"))
+    .mkString
+    .split('\n')
+    .toList
+
+  final case class Monkey(
+    operation: Long => Long,
+    testDiv: Long,
+    targetTrue: Int,
+    targetFalse: Int,
+    items: List[Long],
+    inspected: Int = 0)
+
+  val monkeys = input
+    .grouped(7)
+    .toList
+    .map(_.filter(_.nonEmpty))
+    .map(lines =>
+      Monkey(
+        lines(2).split(" ").takeRight(3) match
+          case Array("old", "*", "old") => old => old * old
+          case Array("old", "+", "old") => old => old + old
+          case Array("old", "+", value) => _ + value.toInt
+          case Array("old", "*", value) => _ * value.toInt
+        ,
+        lines(3).split(" ").last.toInt,
+        lines(4).split(" ").last.toInt,
+        lines(5).split(" ").last.toInt,
+        lines(1).split(": ").last.split(", ").map(_.toInt).toList.map(_.toLong)
+      )
+    ).toList
+
+  val part1 = (0 until (monkeys.length * 20))
+    .map(_ % (monkeys.length))
+    .foldLeft(monkeys)((monkeys, i) =>
+      val m = monkeys(i)
+      m.items
+        .foldLeft(monkeys) { case (monkeys, item) =>
+          val newItem  = m.operation(item)
+          val receiver = if (newItem / 3) % m.testDiv == 0 then m.targetTrue else m.targetFalse
+          val rm       = monkeys(receiver)
+          monkeys.updated(receiver, rm.copy(items = rm.items.appended(newItem / 3)))
+        }
+        .updated(i, m.copy(items = List(), inspected = m.inspected + m.items.length))
+    )
+    .map(_.inspected)
+    .sorted
+    .takeRight(2)
+    .product
+  println("Part 1:")
+  println(part1)
+
+  val modulus = monkeys.map(_.testDiv).product
+
+  val part2 = (0 until (monkeys.length * 10000))
+    .map(_ % (monkeys.length))
+    .foldLeft(monkeys)((monkeys, i) =>
+      val m = monkeys(i)
+      m.items
+        .foldLeft(monkeys) { case (monkeys, item) =>
+          val newItem  = m.operation(item) % modulus
+          val receiver = if newItem % m.testDiv == 0 then m.targetTrue else m.targetFalse
+          val rm       = monkeys(receiver)
+
+          monkeys.updated(receiver, rm.copy(items = rm.items.appended(newItem)))
+        }
+        .updated(i, m.copy(items = List(), inspected = m.inspected + m.items.length))
+    )
+    .map(_.inspected)
+    .sorted
+    .takeRight(2)
+    .map(_.toLong)
+    .product
+  println("Part 2:")
+  println(part2)
+end Day11