Solution 2018-15, part 2 (Beverage Bandits)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2018/day15/BeverageBandits.kt

@@ -10,7 +10,7 @@ import io.github.oshai.kotlinlogging.KotlinLogging
 
 private val logger = KotlinLogging.logger {}
 
-fun main() = BeverageBandits().run(218272, 0)
+fun main() = BeverageBandits().run(218272, 40861)
 
 class BeverageBandits : AdventOfCode<Int>(2018, 15) {
     override fun part1(input: List<String>): Int {
@@ -22,13 +22,26 @@ class BeverageBandits : AdventOfCode<Int>(2018, 15) {
     }
 
     override fun part2(input: List<String>): Int {
-        return 0
+        var combatArea = CombatArea(input, elfAttackPower = 4)
+        while (true) {
+            while (combatArea.takeOneRound() && !combatArea.anElfDied) {
+                // the action takes place in the condition
+            }
+            if (combatArea.anElfDied) {
+                combatArea = CombatArea(input, elfAttackPower = combatArea.elfAttackPower + 1)
+            } else {
+                return combatArea.outcome()
+            }
+        }
     }
 }
 
-class CombatArea(input: List<String>) : SimpleCharGrid(input) {
+class CombatArea(input: List<String>, val elfAttackPower: Int = 3) : SimpleCharGrid(input) {
     private val cavern = '.'
-    private val attackPower = 3
+    private val goblinAttackPower = 3
+
+    var anElfDied = false
+        private set
 
     private var fullRounds = 0
     private val units = forEachCoordinates { position, square ->
@@ -39,6 +52,11 @@ class CombatArea(input: List<String>) : SimpleCharGrid(input) {
         }
     }.filterNotNull().toMutableList()
 
+
+    init {
+        logger.info { "starting new combat with attack powers: elfs: $elfAttackPower, goblins: $goblinAttackPower" }
+    }
+
     /**
      * @return if combat continues
      */
@@ -119,14 +137,19 @@ class CombatArea(input: List<String>) : SimpleCharGrid(input) {
             .minByOrNull { it.position }
         if (opponent == null) return
 
-        opponent.hitPoints -= attackPower
+        opponent.hitPoints -= attackPower()
         logger.debug { " $this hit $opponent" }
 
         if (opponent.hitPoints <= 0) {
             opponent.die()
         }
     }
 
+    private fun Player.attackPower() = when (type) {
+        Elf -> elfAttackPower
+        Goblin -> goblinAttackPower
+    }
+
     private fun Player.moveTo(newPosition: Coordinates) {
         logger.debug { " $this moves to $newPosition" }
         setAt(position, cavern)
@@ -138,6 +161,9 @@ class CombatArea(input: List<String>) : SimpleCharGrid(input) {
         logger.debug { " $this died" }
         setAt(position, cavern)
         units.remove(this)
+        if (type == Elf) {
+            anElfDied = true
+        }
     }
 
     private fun logStats() {

src/test/kotlin/de/ronny_h/aoc/year2018/day15/BeverageBanditsTest.kt

@@ -124,17 +124,7 @@ class BeverageBanditsTest : StringSpec({
         combatArea.takeOneRound() shouldBe false
     }
 
-    "part 1: the outcome of the battle of some given examples" {
-        val input2 = """
-            #######
-            #G..#E#
-            #E#E.E#
-            #G.##.#
-            #...#E#
-            #...E.#
-            #######
-        """.asList()
-        val input3 = """
+    val input3 = """
             #######
             #E..EG#
             #.#G.E#
@@ -143,7 +133,7 @@ class BeverageBanditsTest : StringSpec({
             #..E#.#
             #######
         """.asList()
-        val input4 = """
+    val input4 = """
             #######
             #E.G#.#
             #.#G..#
@@ -152,7 +142,7 @@ class BeverageBanditsTest : StringSpec({
             #...E.#
             #######
         """.asList()
-        val input5 = """
+    val input5 = """
             #######
             #.E...#
             #.#..G#
@@ -161,7 +151,7 @@ class BeverageBanditsTest : StringSpec({
             #...#G#
             #######
         """.asList()
-        val input6 = """
+    val input6 = """
             #########
             #G......#
             #.E.#...#
@@ -172,10 +162,22 @@ class BeverageBanditsTest : StringSpec({
             #.....G.#
             #########
         """.asList()
+
+    "part 1: the outcome of the battle of some given examples" {
+        val input2 = """
+            #######
+            #G..#E#
+            #E#E.E#
+            #G.##.#
+            #...#E#
+            #...E.#
+            #######
+        """.asList()
+
         forAll(
             row(input, 27730),
-            row(input2, 36334), // round right, but 3 hit points too high
-            row(input3, 39514), // one round too low, but hit points right
+            row(input2, 36334),
+            row(input3, 39514),
             row(input4, 27755),
             row(input5, 28944),
             row(input6, 18740),
@@ -184,8 +186,15 @@ class BeverageBanditsTest : StringSpec({
         }
     }
 
-    "part 2" {
-        val input = listOf("")
-        BeverageBandits().part2(input) shouldBe 0
+    "part 2: the outcome of the battle with the smallest elf attack power so that no elf dies" {
+        forAll(
+//            row(input, 4988),
+//            row(input3, 31284),
+//            row(input4, 3478),
+//            row(input5, 6474),
+            row(input6, 1140),
+        ) { input, outcome ->
+            BeverageBandits().part2(input) shouldBe outcome
+        }
     }
 })