aoc 2024 day 12 part 1

Author: jacobsandersen

src/main/java/dev/jacobandersen/codechallenges/challenge/adventofcode/year2024/Year2024.java

@@ -4,6 +4,7 @@
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day1.Day1;
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day10.Day10;
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day11.Day11;
+import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day12.Day12;
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day2.Day2;
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day3.Day3;
 import dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day4.Day4;
@@ -28,7 +29,8 @@ public static List<Day> getDays() {
  new Day8(),
  new Day9(),
  new Day10(),
- new Day11()
+ new Day11(),
+ new Day12()
  );
  }
 }

src/main/java/dev/jacobandersen/codechallenges/challenge/adventofcode/year2024/day12/Day12.java

@@ -0,0 +1,107 @@
+package dev.jacobandersen.codechallenges.challenge.adventofcode.year2024.day12;
+
+import dev.jacobandersen.codechallenges.challenge.adventofcode.Day;
+import dev.jacobandersen.codechallenges.util.Direction;
+import dev.jacobandersen.codechallenges.util.Grid;
+import dev.jacobandersen.codechallenges.util.Pair;
+
+import java.util.*;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class Day12 extends Day {
+ public Day12() {
+ super(2024, 12, "Garden Groups");
+ }
+
+ private boolean isInRegion(List<Region> regions, int y, int x) {
+ return regions.stream().anyMatch(rg -> rg.plots.stream().anyMatch(plot -> plot.y == y && plot.x == x));
+ }
+
+ private void exploreFrom(Grid<String> grid, Plot plot, Region region) {
+ if (region.plots.contains(plot)) return; // don't backtrack
+
+ region.plots.add(plot);
+
+ Grid<String> local = grid.copy();
+ for (Direction direction : Direction.cardinalValues()) {
+ final String peek = local.peek(direction);
+ if (peek != null && peek.equals(plot.crop)) {
+ local.move(direction);
+ exploreFrom(local, new Plot(plot.crop, local.getCurrentRow(), local.getCurrentCol()), region);
+ local.move(direction.getOpposite());
+ }
+ }
+ }
+
+ private List<Region> explore(Grid<String> grid) {
+ List<Region> regions = new ArrayList<>();
+
+ for (int y = 0; y < grid.getRows(); y++) {
+ for (int x = 0; x < grid.getCols(); x++) {
+ grid.move(y, x);
+ if (isInRegion(regions, y, x)) continue;
+
+ Region region = new Region(new ArrayList<>());
+ exploreFrom(grid, new Plot(grid.get(), y, x), region);
+ regions.add(region);
+ }
+ }
+
+ return regions;
+ }
+
+ private Grid<String> loadGrid() {
+ return Grid.create(getInputLinesStreamNoBlanks(), str -> Arrays.stream(str.split("")).toList());
+ }
+
+ @Override
+ public String partOne() {
+ return String.valueOf(
+ explore(loadGrid()).stream().mapToInt(Region::fencePrice).sum()
+ );
+ }
+
+ @Override
+ public String partTwo() {
+ Grid<String> grid = loadGrid();
+ List<Region> regions = explore(grid);
+ return String.valueOf(
+ regions.stream().mapToInt(Region::discountedFencePrice).sum()
+ );
+ }
+
+ record Plot(String crop, int y, int x) {
+ }
+
+ record Region(List<Plot> plots) {
+ public int area() {
+ return plots.size();
+ }
+
+ public int perimeter() {
+ final Set<Pair<Integer, Integer>> points = plots.stream().map(plot -> Pair.of(plot.y, plot.x)).collect(Collectors.toSet());
+ return points.stream().mapToInt(pt -> {
+ int perimeter = 4;
+ for (final Direction direction : Direction.cardinalValues()) {
+ final Pair<Integer, Integer> rel = direction.relativeCoordinate();
+ final Pair<Integer, Integer> neighbor = Pair.of(pt.first() + rel.first(), pt.second() + rel.second());
+ if (points.contains(neighbor)) perimeter--;
+ }
+ return perimeter;
+ }).sum();
+ }
+
+ public int fencePrice() {
+ return area() * perimeter();
+ }
+
+ public int sides() {
+ return 0;
+ }
+
+ public int discountedFencePrice() {
+ return area() * sides();
+ }
+ }
+}

src/main/java/dev/jacobandersen/codechallenges/util/Direction.java

@@ -33,6 +33,16 @@ public final Direction getOpposite() {
  };
  }
 
+ public final Direction getCardinalLeft() {
+ return switch (this) {
+ case NORTH -> WEST;
+ case WEST -> SOUTH;
+ case SOUTH -> EAST;
+ case EAST -> NORTH;
+ default -> this;
+ };
+ }
+
  public final Direction getCardinalRight() {
  return switch (this) {
  case NORTH -> EAST;

src/main/java/dev/jacobandersen/codechallenges/util/Grid.java

@@ -209,6 +209,10 @@ public Grid<T> copy() {
  return new Grid<>(rows, cols, currentRow, currentCol, copy);
  }
 
+ public boolean contains(Pair<Integer, Integer> position) {
+ return position.first() >= 0 && position.first() < rows && position.second() >= 0 && position.second() < cols;
+ }
+
  @Override
  public String toString() {
  StringBuilder builder = new StringBuilder("Grid {\n" +