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day 14 part 1
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‎src/main/java/com/codefork/aoc2024/day14/Part01.java

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package com.codefork.aoc2024.day14;
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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(int width, int height, Stream<String> data) {
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var swarm = Swarm.create(data, width, height);
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var finalSwarm = swarm.doMoves(100);
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return String.valueOf(finalSwarm.getSafetyFactor());
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}
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@Override
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public String solve() {
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Assert.assertEquals("12", solve(11, 7, getSampleInput()));
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return solve(101, 103, 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/day14/Swarm.java

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package com.codefork.aoc2024.day14;
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import com.codefork.aoc2024.util.Maps;
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import java.util.List;
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import java.util.Map;
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import java.util.regex.Pattern;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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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 Swarm(List<Robot> robots, int width, int height) {
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public record Position(int x, int y) {
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}
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public record Velocity(int dx, int dy) {
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}
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public record Robot(Position position, Velocity v) {
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}
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private final static Pattern pat = Pattern.compile("p=([0-9]+),([0-9]+) v=([0-9\\-]+),([0-9\\-]+)");
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public static Swarm create(Stream<String> data, int width, int height) {
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var robots = data
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.map(line -> {
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var matcher = pat.matcher(line);
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if (!matcher.find()) {
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throw new RuntimeException("couldn't parse line");
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}
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var parts = IntStream.range(1, 5)
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.mapToObj(matcher::group)
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.map(Integer::valueOf)
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.toList();
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return new Robot(new Position(parts.get(0), parts.get(1)), new Velocity(parts.get(2), parts.get(3)));
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})
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.toList();
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return new Swarm(robots, width, height);
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}
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public Swarm doMoves(int n) {
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var finalRobots = IntStream.range(0, n)
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.boxed()
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.collect(foldLeft(
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() -> robots,
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(acc, i) -> {
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return acc.stream().map(this::move).toList();
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}
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));
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return new Swarm(finalRobots, width, height);
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}
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public Robot move(Robot robot) {
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var changedX = robot.position().x() + robot.v().dx();
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var newX = changedX >= width ? changedX - width : (changedX < 0 ? changedX + width : changedX);
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var changedY = (robot.position().y() + robot.v().dy()) % height;
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var newY = changedY >= height ? changedY - height : (changedY < 0 ? changedY + height : changedY);
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return new Robot(new Position(newX, newY), robot.v());
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}
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public void print() {
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var byPos = robots().stream().collect(Collectors.toMap(
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Robot::position,
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List::of,
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Maps::listConcat));
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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 list = byPos.getOrDefault(new Position(x, y), List.of());
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var count = list.size();
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var ch = count > 0 ? String.valueOf(count) : ".";
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System.out.print(ch);
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}
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System.out.println();
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}
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}
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private static int DISCARD = -1;
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/**
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* quadrants are numbered in order from left to right, then top to bottom, like reading English
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* @return
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*/
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public Map<Integer, Integer> getQuadrantCounts() {
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var byQuadrant = robots.stream()
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.collect(Collectors.groupingBy(
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(robot) -> {
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if (robot.position().y() < height / 2) {
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if (robot.position().x() < width / 2) {
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return 0;
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} else if (robot.position().x() > width / 2) {
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return 1;
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}
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} else if (robot.position().y() > height / 2) {
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if (robot.position().x() < width / 2) {
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return 2;
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} else if (robot.position().x() > width / 2) {
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return 3;
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}
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}
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// put the robots on the center lines in a separate group
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// that we'll discard
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return DISCARD;
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})
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);
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return byQuadrant.entrySet().stream()
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.filter(entry -> entry.getKey() != DISCARD)
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.collect(Collectors.toMap(
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Map.Entry::getKey,
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entry -> entry.getValue().size(),
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Integer::sum
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));
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}
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/**
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* testing for part 2: try smaller sections
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*/
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public Map<Integer, Integer> getCustomSectionCounts() {
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var byQuadrant = robots.stream()
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.collect(Collectors.groupingBy(
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(robot) -> {
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if (robot.position().y() < height / 3) {
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if (robot.position().x() < width / 2) {
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return 0;
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} else if (robot.position().x() > width / 2) {
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return 1;
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}
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} else if (robot.position().y() > height / 3 && robot.position().y() < (height / 3) * 2) {
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if (robot.position().x() < width / 2) {
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return 2;
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} else if (robot.position().x() > width / 2) {
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return 3;
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}
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} else if (robot.position().y() > (height / 3) * 2) {
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if (robot.position().x() < width / 2) {
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return 4;
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} else if (robot.position().x() > width / 2) {
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return 5;
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}
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}
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// put the robots on the center lines in a separate group
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// that we'll discard
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return DISCARD;
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})
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);
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return byQuadrant.entrySet().stream()
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.filter(entry -> entry.getKey() != DISCARD)
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.collect(Collectors.toMap(
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Map.Entry::getKey,
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entry -> {
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// count occupied positions rather than robots, since they can be stacked, and we only
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// care about what they look like from above
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record Pos(int x, int y) {
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}
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var list = entry.getValue();
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var occupiedPositions = list.stream()
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.map(robot -> new Pos(robot.position().x(), robot.position().y()))
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.collect(Collectors.toSet());
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return occupiedPositions.size();
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},
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Integer::sum
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));
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}
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public int getSafetyFactor() {
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return getQuadrantCounts().entrySet().stream()
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.reduce(1, (acc, entry) -> acc * entry.getValue(), Integer::sum);
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}
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}

‎src/main/resources/day14/input

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‎src/main/resources/day14/sample

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