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day 15
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‎README.md

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@@ -80,3 +80,7 @@ Today I randomly discovered
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[local classes](https://docs.oracle.com/javase/tutorial/java/javaOO/localclasses.html) and
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[records](https://docs.oracle.com/en/java/javase/17/language/records.html). This allows you to scope, say, an intermediate record for a stream transformation, to a single method
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and avoid clutter at the class level. Pretty cool!
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### 12/15/2024
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Day 14 Part 2 had me stumped, at least for now. Moving on to Day 15.

‎src/main/java/com/codefork/aoc2024/day15/Box.java

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package com.codefork.aoc2024.day15;
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public record Box(Position pos, int width) {
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}

‎src/main/java/com/codefork/aoc2024/day15/Direction.java

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package com.codefork.aoc2024.day15;
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public enum Direction {
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Up, Right, Down, Left;
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public static Direction parse(String s) {
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return switch (s) {
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case "^" -> Up;
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case ">" -> Right;
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case "v" -> Down;
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case "<" -> Left;
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default -> throw new RuntimeException("unrecognized direction");
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};
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}
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}

‎src/main/java/com/codefork/aoc2024/day15/Document.java

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package com.codefork.aoc2024.day15;
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import com.codefork.aoc2024.util.WithIndex;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.stream.Stream;
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import static com.codefork.aoc2024.util.FoldLeft.foldLeft;
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public record Document(Warehouse warehouse, List<Direction> moves) {
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private static final List<String> mapChars = List.of("O", "#", "@", ".");
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/**
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* @param data
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* @param width interpret walls and boxes to be as wide as this value
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* @return
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*/
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public static Document parse(Stream<String> data, int width) {
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return data
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.map(WithIndex.indexed())
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.filter(lineWithIndex -> !lineWithIndex.value().isEmpty())
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.collect(foldLeft(
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() -> new Document(new Warehouse(new HashSet<>(), new HashSet<>(), new Position(-1, -1)), new ArrayList<>()),
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(acc, lineWithIndex) -> {
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var y = lineWithIndex.index();
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var line = lineWithIndex.value();
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if (mapChars.stream().anyMatch(line::contains)) {
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return line.chars()
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.boxed()
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.map(WithIndex.indexed())
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.collect(foldLeft(
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() -> acc,
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(acc2, chWithIndex) -> {
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var x = chWithIndex.index() * width;
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var ch = String.valueOf((char) chWithIndex.value().intValue());
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var pos = new Position(x, y);
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switch (ch) {
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case "#" -> {
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var newWalls = new HashSet<>(acc2.warehouse().walls());
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for (var n = 0; n < width; n++) {
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newWalls.add(new Position(pos.x() + n, pos.y()));
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}
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return new Document(acc2.warehouse().withWalls(newWalls), acc2.moves());
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}
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case "O" -> {
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var newBoxes = new HashSet<>(acc2.warehouse().boxes());
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newBoxes.add(new Box(pos, width));
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return new Document(acc2.warehouse().withBoxes(newBoxes), acc2.moves());
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}
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case "@" -> {
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return new Document(acc2.warehouse().withRobot(pos), acc2.moves());
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}
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}
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return acc2;
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})
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);
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} else {
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return line.chars()
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.boxed()
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.collect(foldLeft(
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() -> acc,
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(acc2, charInt) -> {
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var ch = String.valueOf((char) charInt.intValue());
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var dir = Direction.parse(ch);
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var newMoves = acc2.moves();
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newMoves.add(dir);
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return new Document(acc2.warehouse(), newMoves);
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})
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);
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}
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})
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);
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}
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/**
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* do all the moves and return the final state of the warehouse
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**/
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public Warehouse doMoves() {
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return moves().stream()
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.collect(foldLeft(
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this::warehouse,
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Warehouse::move)
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);
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}
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}

‎src/main/java/com/codefork/aoc2024/day15/Part01.java

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package com.codefork.aoc2024.day15;
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import com.codefork.aoc2024.Problem;
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import com.codefork.aoc2024.util.Assert;
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import java.util.stream.Stream;
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public class Part01 extends Problem {
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public String solve(Stream<String> data) {
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var document = Document.parse(data, 1);
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var finalWarehouse = document.doMoves();
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return String.valueOf(finalWarehouse.getSumBoxCoordinates());
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}
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@Override
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public String solve() {
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Assert.assertEquals("2028", solve(getFileAsStream("small_sample")));
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Assert.assertEquals("10092", solve(getSampleInput()));
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return solve(getInput());
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}
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public static void main(String[] args) {
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new Part01().run();
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}
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}

‎src/main/java/com/codefork/aoc2024/day15/Part02.java

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package com.codefork.aoc2024.day15;
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import com.codefork.aoc2024.Problem;
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import com.codefork.aoc2024.util.Assert;
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import java.util.stream.Stream;
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public class Part02 extends Problem {
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public String solve(Stream<String> data) {
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var document = Document.parse(data, 2);
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var finalWarehouse = document.doMoves();
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return String.valueOf(finalWarehouse.getSumBoxCoordinates());
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}
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@Override
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public String solve() {
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Assert.assertEquals("9021", solve(getSampleInput()));
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return solve(getInput());
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}
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public static void main(String[] args) {
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new Part02().run();
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}
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}

‎src/main/java/com/codefork/aoc2024/day15/Position.java

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package com.codefork.aoc2024.day15;
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public record Position(int x, int y) {
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public Position withChangedX(int dX) {
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return new Position(x() + dX, y());
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}
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public Position withChangedY(int dY) {
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return new Position(x(), y() + dY);
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}
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}

‎src/main/java/com/codefork/aoc2024/day15/Warehouse.java

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package com.codefork.aoc2024.day15;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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import java.util.stream.IntStream;
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import java.util.stream.Stream;
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public record Warehouse(Set<Position> walls, Set<Box> boxes, Position robot) {
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public Warehouse withWalls(Set<Position> newWalls) {
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return new Warehouse(newWalls, boxes, robot);
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}
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public Warehouse withBoxes(Set<Box> newBoxes) {
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return new Warehouse(walls, newBoxes, robot);
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}
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public Warehouse withRobot(Position newRobot) {
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return new Warehouse(walls, boxes, newRobot);
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}
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/**
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* return true if any of the positions are walls
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*/
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public boolean areWalls(List<Position> positions) {
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return positions.stream().anyMatch(walls::contains);
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}
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public Warehouse moveVertical(int dY) {
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var boxWidth = boxes.stream().findFirst().orElseThrow().width();
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var foundEmpty = false;
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// order matters for boxesToMove, so it's a List
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var boxesToMove = new ArrayList<Box>();
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var boxesToCheck = IntStream.range(0, boxWidth).boxed().map(i ->
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new Position(robot.x() - i, robot.y() + dY)
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).toList();
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var wallsToCheck = List.of(new Position(robot.x(), robot.y() + dY));
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while (!areWalls(wallsToCheck)) {
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// check if boxesToCheck are boxes
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final var _toCheck = boxesToCheck;
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var foundBoxes = boxes.stream().filter(box -> _toCheck.contains(box.pos())).toList();
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// no boxes found? we're done, we can move!
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if(foundBoxes.isEmpty()) {
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foundEmpty = true;
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break;
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}
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boxesToMove.addAll(foundBoxes);
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// set boxesToCheck for the boxes we just found
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boxesToCheck = foundBoxes.stream().flatMap(box -> {
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// TODO: I hard coded these possibilities because I'm tired,
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// but they should really be calculated based on boxWidth
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if(boxWidth == 1) {
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return Stream.of(box.pos().withChangedY(dY));
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} else if(boxWidth == 2) {
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return Stream.of(
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box.pos().withChangedY(dY).withChangedX(-1),
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box.pos().withChangedY(dY),
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box.pos().withChangedY(dY).withChangedX(1)
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);
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}
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throw new RuntimeException("can't handle boxWidth=" + boxWidth);
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}).toList();
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wallsToCheck = foundBoxes.stream().flatMap(box -> {
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// TODO: I hard coded these possibilities because I'm tired,
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// but they should really be calculated based on boxWidth
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if(boxWidth == 1) {
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return Stream.of(box.pos().withChangedY(dY));
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} else if(boxWidth == 2) {
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return Stream.of(box.pos().withChangedY(dY), box.pos().withChangedY(dY).withChangedX(1));
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}
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throw new RuntimeException("can't handle boxWidth=" + boxWidth);
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}).toList();
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}
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if (foundEmpty) {
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var newBoxes = new HashSet<>(boxes);
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for (var box : boxesToMove.reversed()) {
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newBoxes.remove(box);
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newBoxes.add(new Box(new Position(box.pos().x(), box.pos().y() + dY), boxWidth));
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}
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return new Warehouse(walls, newBoxes, new Position(robot.x(), robot.y() + dY));
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} else {
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return this;
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}
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}
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public Warehouse moveHorizontal(int dX) {
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var boxWidth = boxes.stream().findFirst().orElseThrow().width();
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var foundEmpty = false;
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// order matters for boxesToMove, so it's a List
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var boxesToMove = new ArrayList<Box>();
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var boxToCheck = dX < 0 ?
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new Box(new Position(robot.x() + (dX * boxWidth), robot.y()), boxWidth) :
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new Box(new Position(robot.x() + dX, robot.y()), boxWidth);
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var wallsToCheck = List.of(new Position(robot.x() + dX, robot.y()));
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while (!areWalls(wallsToCheck)) {
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var isBox = boxes.contains(boxToCheck);
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// not a box? we found empty space, so we can move
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if(!isBox) {
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foundEmpty = true;
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break;
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}
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boxesToMove.add(boxToCheck);
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boxToCheck = new Box(new Position(boxToCheck.pos().x() + (dX * boxWidth), boxToCheck.pos().y()), boxWidth);
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// TODO: I hard coded these possibilities because I'm tired,
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// but they should really be calculated based on boxWidth
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if(boxWidth == 1) {
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wallsToCheck = List.of(boxToCheck.pos());
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} else if (boxWidth == 2) {
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wallsToCheck = dX < 0 ?
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List.of(boxToCheck.pos().withChangedX(1)) :
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List.of(boxToCheck.pos());
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}
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}
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if (foundEmpty) {
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var newBoxes = new HashSet<>(boxes);
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for (var box : boxesToMove.reversed()) {
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newBoxes.remove(box);
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var moved = new Box(new Position(box.pos().x() + dX, box.pos().y()), boxWidth);
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newBoxes.add(moved);
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}
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return new Warehouse(walls, newBoxes, new Position(robot.x() + dX, robot.y()));
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} else {
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return this;
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}
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}
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/**
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* move the robot in the specified direction and return the new state of the warehouse
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* @param direction
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* @return
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*/
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public Warehouse move(Direction direction) {
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var newWarehouse = switch (direction) {
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case Direction.Up -> moveVertical(-1);
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case Direction.Down -> moveVertical(1);
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case Direction.Right -> moveHorizontal(1);
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case Direction.Left -> moveHorizontal(-1);
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};
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//System.out.println("moved " + direction + ":");
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//newWarehouse.print();
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return newWarehouse;
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}
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public int getSumBoxCoordinates() {
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return boxes.stream()
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.map(box -> 100 * box.pos().y() + box.pos().x())
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.mapToInt(i -> i)
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.sum();
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}
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public void print() {
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int height = walls.stream().map(Position::y).max(Integer::compareTo).orElseThrow() + 1;
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int width = walls.stream().map(Position::x).max(Integer::compareTo).orElseThrow() + 1;
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for (var y = 0; y < height; y++) {
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for (var x = 0; x < width; x++) {
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var pos = new Position(x, y);
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if (walls.contains(pos)) {
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System.out.print("#");
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} else if (boxes.contains(new Box(pos, 1))) {
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System.out.print("O");
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} else if (boxes.contains(new Box(pos, 2))) {
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System.out.print("[]");
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x += 1;
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} else if (pos.equals(robot)) {
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System.out.print("@");
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} else {
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System.out.print(".");
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}
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}
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System.out.println();
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}
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}
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}

‎src/main/resources/day15/input

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‎src/main/resources/day15/sample

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‎src/main/resources/day15/small_sample

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