Year 2015 Day 21

Author: maneatingape

README.md

@@ -230,3 +230,4 @@ The minimal SBT project provides:
 | 18 | [Like a GIF For Your Yard](https://adventofcode.com/2015/day/18) | [Source](src/main/scala/AdventOfCode2015/Day18.scala) |
 | 19 | [Medicine for Rudolph](https://adventofcode.com/2015/day/19) | [Source](src/main/scala/AdventOfCode2015/Day19.scala) |
 | 20 | [Infinite Elves and Infinite Houses](https://adventofcode.com/2015/day/20) | [Source](src/main/scala/AdventOfCode2015/Day20.scala) |
+| 21 | [RPG Simulator 20XX](https://adventofcode.com/2015/day/21) | [Source](src/main/scala/AdventOfCode2015/Day21.scala) |

src/main/resources/AdventOfCode2015/Day21.txt

@@ -0,0 +1,3 @@
+Hit Points: 100
+Damage: 8
+Armor: 2

src/main/scala/AdventOfCode2015/Day21.scala

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+package AdventOfCode2015
+
+object Day21:
+  case class Item(cost: Int, damage: Int, armor: Int):
+    def +(other: Item): Item = Item(cost + other.cost, damage + other.damage, armor + other.armor)
+
+  val none = Item(0, 0, 0)
+  val weapons = Set(Item(8, 4, 0), Item(10, 5, 0), Item(25, 6, 0), Item(40, 7, 0), Item(74, 8, 0))
+  val armors = Set(none, Item(13, 0, 1), Item(31, 0, 2), Item(53, 0, 3), Item(75, 0, 4), Item(102, 0, 5))
+  val rings = Seq(none, none, Item(25, 1, 0), Item(50, 2, 0), Item(100, 3, 0), Item(20, 0, 1), Item(40, 0, 2), Item(80, 0, 3))
+    .combinations(2).map(c => c.head + c.last).toSet
+  val outfits = for weapon <- weapons; armor <- armors; ring <- rings yield weapon + armor + ring
+
+  def parse(input: Seq[String]): Item =
+    val Seq(health, damage, armor) = input.map(_.filter(_.isDigit).toInt)
+    Item(health, damage, armor)
+
+  def fight(boss: Item)(hero: Item): Boolean =
+    val heroTurns = boss.cost / (hero.damage - boss.armor).max(1)
+    val bossTurns = 100 / (boss.damage - hero.armor).max(1)
+    heroTurns <= bossTurns
+
+  def part1(input: Seq[String]): Int =
+    val boss = parse(input)
+    outfits.filter(fight(boss)).map(_.cost).min
+
+  def part2(input: Seq[String]): Int =
+    val boss = parse(input)
+    outfits.filterNot(fight(boss)).map(_.cost).max
+
+  def main(args: Array[String]): Unit =
+    val data = io.Source.fromResource("AdventOfCode2015/Day21.txt").getLines().toSeq
+    println(part1(data))
+    println(part2(data))

src/test/scala/AdventOfCode2015/Day21Suite.scala

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+package AdventOfCode2015
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Day21Suite extends AnyFunSuite
+// No unit tests possible