Day 21 2020 (#222)

src/main/kotlin/me/peckb/aoc/_2020/calendar/day21/Day21.kt

@@ -0,0 +1,103 @@
+package me.peckb.aoc._2020.calendar.day21
+
+import javax.inject.Inject
+
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+
+class Day21 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).readAs(::food) { input ->
+    val (allergenToPossibilities, nonAllergenIngredientCounts) = generatePossibilitiesAndCounts(input)
+
+    allergenToPossibilities.forEach { (_, ingredientPossibilityCounts) ->
+      val sortedByCounts = ingredientPossibilityCounts.entries.sortedByDescending { it.value }
+      val topCountValue = sortedByCounts.first().value
+
+      val mightBe = sortedByCounts.filter { it.value == topCountValue }
+
+      mightBe.forEach {
+        nonAllergenIngredientCounts.remove(it.key)
+      }
+    }
+
+    nonAllergenIngredientCounts.entries.sumOf { it.value }
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).readAs(::food) { input ->
+    val (allergenToPossibilities, _) = generatePossibilitiesAndCounts(input)
+
+    val probableAllergenIngredients = mutableMapOf<String, MutableMap<String, Int>>()
+
+    allergenToPossibilities.forEach { (allergen, ingredientPossibilityCounts) ->
+      val sortedByCounts = ingredientPossibilityCounts.entries.sortedByDescending { it.value }
+      val topCountValue = sortedByCounts.first().value
+
+      val mightBe= sortedByCounts.filter { it.value == topCountValue }
+
+      probableAllergenIngredients[allergen] = mightBe.associateBy({it.key}, {it.value}).toMutableMap()
+    }
+
+    val ingredientWithAllergen = mutableMapOf<String, String>()
+    while (probableAllergenIngredients.isNotEmpty()) {
+      val (guaranteedValues, valuesStillUnknown) = probableAllergenIngredients.entries.partition { it.value.count() == 1 }
+
+      guaranteedValues.forEach { (allergen, ingredientMap) ->
+        val ingredient = ingredientMap.entries.first().key
+
+        ingredientWithAllergen[allergen] = ingredient
+
+        valuesStillUnknown.forEach { (_, ingredientPossibilities) ->
+          ingredientPossibilities.remove(ingredient)
+        }
+      }
+
+      guaranteedValues.forEach {
+        probableAllergenIngredients.remove(it.key)
+      }
+    }
+
+    ingredientWithAllergen.toSortedMap().values.joinToString(",")
+  }
+
+  private fun food(line: String): Food {
+    val (ingredientsString, allergensString) = line.split(" (contains ")
+    val ingredients = ingredientsString.split(" ")
+    val allergens = allergensString.dropLast(1).split(", ")
+
+    return Food(ingredients, allergens)
+  }
+
+  private fun generatePossibilitiesAndCounts(input: Sequence<Food>): FoodContents {
+    val allergenToPossibilities = mutableMapOf<String, MutableMap<String, Int>>()
+    val nonAllergenIngredientCounts = mutableMapOf<String, Int>()
+
+    input.forEach { (ingredients, allergens) ->
+      ingredients.forEach { i ->  nonAllergenIngredientCounts.merge(i, 1, Int::plus) }
+      allergens.forEach { allergen ->
+        allergenToPossibilities.merge(
+          allergen,
+          ingredients.associateWith { 1 }.toMutableMap()
+        ) { originalMap, newMap ->
+          originalMap.apply {
+            newMap.forEach { (ingredient, count) ->
+              this.merge(ingredient, count, Int::plus)
+            }
+          }
+        }
+      }
+    }
+
+    return FoodContents(allergenToPossibilities, nonAllergenIngredientCounts)
+  }
+
+  data class FoodContents(
+    val allergenToPossibilities: MutableMap<String, MutableMap<String, Int>>,
+    val nonAllergenIngredientCounts: MutableMap<String, Int>
+  )
+
+  data class Food(
+    val ingredients: List<String>,
+    val allergens: List<String>
+  )
+}

src/main/kotlin/me/peckb/aoc/_2020/calendar/day21/README.md

@@ -0,0 +1 @@
+## [Day 21: Allergen Assessment](https://adventofcode.com/2020/day/21)

src/test/kotlin/me/peckb/aoc/_2020/TestDayComponent.kt

@@ -20,6 +20,7 @@ import me.peckb.aoc._2020.calendar.day17.Day17Test
 import me.peckb.aoc._2020.calendar.day18.Day18Test
 import me.peckb.aoc._2020.calendar.day19.Day19Test
 import me.peckb.aoc._2020.calendar.day20.Day20Test
+import me.peckb.aoc._2020.calendar.day21.Day21Test
 import javax.inject.Singleton
 
 import me.peckb.aoc.DayComponent
@@ -49,4 +50,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day18Test: Day18Test)
   fun inject(day19Test: Day19Test)
   fun inject(day20Test: Day20Test)
+  fun inject(day21Test: Day21Test)
 }

src/test/kotlin/me/peckb/aoc/_2020/calendar/day21/Day21Test.kt

@@ -0,0 +1,33 @@
+package me.peckb.aoc._2020.calendar.day21
+
+import javax.inject.Inject
+
+
+import me.peckb.aoc._2020.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day21Test {
+  @Inject
+  lateinit var day21: Day21
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay21PartOne() {
+    assertEquals(2786, day21.partOne(DAY_21))
+  }
+
+  @Test
+  fun testDay21PartTwo() {
+    assertEquals("prxmdlz,ncjv,knprxg,lxjtns,vzzz,clg,cxfz,qdfpq", day21.partTwo(DAY_21))
+  }
+
+  companion object {
+    private const val DAY_21: String = "advent-of-code-input/2020/day21.input"
+  }
+}