Day 6

l0s · l0s · commit fb909b599acb · 2021-12-05T21:50:25.000-08:00
diff --git a/src/test/java/com/macasaet/Day06.java b/src/test/java/com/macasaet/Day06.java
@@ -0,0 +1,120 @@
+package com.macasaet;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * --- Day 6: Lanternfish ---
+ */
+public class Day06 {
+
+    /**
+     * A glowing fish that spawns very quickly. Their population grows exponentially.
+     */
+    public static class Lanternfish {
+
+        private int daysToSpawn;
+
+        /**
+         * @param daysToSpawn the number of days until it creates a new {@link Lanternfish}
+         */
+        public Lanternfish(final int daysToSpawn) {
+            setDaysToSpawn(daysToSpawn);
+        }
+
+        /**
+         * Simulate the passage of one day
+         *
+         * @return either a new Lanternfish or nothing depending on whether the fish spawned
+         */
+        public Optional<Lanternfish> tick() {
+            final var timer = getDaysToSpawn() - 1;
+            if (timer < 0) {
+                setDaysToSpawn(6);
+                return Optional.of(new Lanternfish(8));
+            } else {
+                setDaysToSpawn(timer);
+                return Optional.empty();
+            }
+        }
+
+        /**
+         * @return the number of days until the fish spawns
+         */
+        public int getDaysToSpawn() {
+            return this.daysToSpawn;
+        }
+
+        /**
+         * Update this fish's days to spawn
+         *
+         * @param daysToSpawn the number of days until the fish spawns, must be non-negative
+         */
+        protected void setDaysToSpawn(final int daysToSpawn) {
+            if (daysToSpawn < 0) {
+                throw new IllegalArgumentException("\"days to spawn\" must be non-negative");
+            }
+            this.daysToSpawn = daysToSpawn;
+        }
+    }
+
+    protected Stream<String> getInput() {
+        return StreamSupport
+                .stream(new LineSpliterator("day-06.txt"),
+                        false);
+    }
+
+    public List<Lanternfish> parseInput() {
+        final var list = getInput().toList();
+        final var line = list.get(0);
+        final var components = line.split(",");
+        return Arrays.stream(components)
+                .mapToInt(Integer::parseInt)
+                .mapToObj(Lanternfish::new)
+                .collect(Collectors.toList());
+    }
+
+    @Test
+    public final void part1() {
+        var population = parseInput();
+        for (int _i = 80; --_i >= 0; ) {
+            final List<Lanternfish> list = new ArrayList<>(population);
+            for (final var fish : population) {
+                final var result = fish.tick();
+                result.ifPresent(list::add);
+            }
+            population = list;
+        }
+        System.out.println("Part 1: " + population.size());
+    }
+
+    @Test
+    public final void part2() {
+        final var initial = parseInput();
+        var map = new long[9];
+        for (final var fish : initial) {
+            map[fish.getDaysToSpawn()]++;
+        }
+        for (int _i = 256; --_i >= 0; ) {
+            final var temp = new long[map.length];
+            for (int daysToSpawn = map.length; --daysToSpawn >= 0; ) {
+                final var count = map[daysToSpawn];
+                final var prototype = new Lanternfish(daysToSpawn);
+                final var result = prototype.tick();
+                temp[prototype.getDaysToSpawn()] += count;
+                result.ifPresent(spawn -> temp[spawn.getDaysToSpawn()] = temp[spawn.getDaysToSpawn()] + count);
+            }
+            map = temp;
+        }
+        final var result = Arrays.stream(map).reduce(0L, Long::sum);
+        System.out.println("Part 2: " + result);
+    }
+
+}
diff --git a/src/test/resources/sample/day-06.txt b/src/test/resources/sample/day-06.txt
@@ -0,0 +1 @@
+3,4,3,1,2
