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Day 20
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‎src/test/java/com/macasaet/Day20.java

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package com.macasaet;
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import static org.junit.jupiter.api.Assertions.*;
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import java.util.*;
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import java.util.stream.Stream;
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import java.util.stream.StreamSupport;
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import org.junit.jupiter.api.Nested;
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import org.junit.jupiter.api.Test;
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/**
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* --- Day 20: Trench Map ---
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*/
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public class Day20 {
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protected Stream<String> getInput() {
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return StreamSupport
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.stream(new LineSpliterator("day-20.txt"),
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false);
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}
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public record ImageEnhancementAlgorithm(boolean[] map) {
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public boolean isPixelLit(final int code) {
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return map()[code];
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}
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public static ImageEnhancementAlgorithm parse(final String line) {
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final var map = new boolean[line.length()];
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for (int i = line.length(); --i >= 0; map[i] = line.charAt(i) == '#') ;
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return new ImageEnhancementAlgorithm(map);
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}
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}
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protected record Coordinate(int x, int y) {
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}
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public record Image(SortedMap<Integer, SortedMap<Integer, Boolean>> pixels, int minX, int maxX, int minY,
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int maxY, boolean isEven) {
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public Image enhance(final ImageEnhancementAlgorithm algorithm) {
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final var enhancedPixelMap = new TreeMap<Integer, SortedMap<Integer, Boolean>>();
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int enhancedMinX = minX;
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int enhancedMaxX = maxX;
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int enhancedMinY = minY;
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int enhancedMaxY = maxY;
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for (int i = minX - 1; i <= maxX + 1; i++) {
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final var targetRow = new TreeMap<Integer, Boolean>();
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for (int j = minY - 1; j <= maxY + 1; j++) {
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final int replacementId = decode(i, j, !isEven && algorithm.isPixelLit(0));
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final var shouldLight = algorithm.isPixelLit(replacementId);
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if (shouldLight) {
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// save space by only storing an entry when lit
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targetRow.put(j, true);
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enhancedMinY = Math.min(enhancedMinY, j);
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enhancedMaxY = Math.max(enhancedMaxY, j);
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}
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}
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if (!targetRow.isEmpty()) {
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// save space by only storing a row if at least one cell is lit
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enhancedPixelMap.put(i, Collections.unmodifiableSortedMap(targetRow));
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enhancedMinX = Math.min(enhancedMinX, i);
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enhancedMaxX = Math.max(enhancedMaxX, i);
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}
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}
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return new Image(Collections.unmodifiableSortedMap(enhancedPixelMap), enhancedMinX, enhancedMaxX, enhancedMinY, enhancedMaxY, !isEven);
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}
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int decode(final int x, final int y, boolean voidIsLit) {
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final var list = getNeighbouringCoordinates(x, y).stream()
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.map(coordinate -> isBitSet(coordinate, voidIsLit))
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.toList();
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int result = 0;
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for (int i = list.size(); --i >= 0; ) {
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if (list.get(i)) {
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final int shiftDistance = list.size() - i - 1;
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result |= 1 << shiftDistance;
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}
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}
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if (result < 0 || result > 512) {
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throw new IllegalStateException("Unable to decode pixel at " + x + ", " + y);
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}
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return result;
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}
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boolean isBitSet(final Coordinate coordinate, boolean voidIsLit) {
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final var row = pixels().get(coordinate.x());
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if((coordinate.x() < minX || coordinate.x() > maxX) && row == null) {
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return voidIsLit;
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}
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else if(row == null) {
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return false;
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}
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return row.getOrDefault(coordinate.y(), (coordinate.y() < minY || coordinate.y() > maxY) && voidIsLit);
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}
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List<Coordinate> getNeighbouringCoordinates(int x, int y) {
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return Arrays.asList(
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new Coordinate(x - 1, y - 1),
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new Coordinate(x - 1, y),
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new Coordinate(x - 1, y + 1),
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new Coordinate(x, y - 1),
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new Coordinate(x, y),
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new Coordinate(x, y + 1),
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new Coordinate(x + 1, y - 1),
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new Coordinate(x + 1, y),
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new Coordinate(x + 1, y + 1)
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);
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}
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public long countLitPixels() {
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return pixels().values()
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.stream()
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.flatMap(row -> row.values().stream())
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.filter(isLit -> isLit)
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.count();
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}
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public int width() {
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return maxX - minX + 1;
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}
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public int height() {
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return maxY - minY + 1;
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}
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public String toString() {
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final var builder = new StringBuilder();
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builder.append(width()).append('x').append(height()).append('\n');
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for (int i = minX; i <= maxX; i++) {
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final var row = pixels.getOrDefault(i, Collections.emptySortedMap());
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for (int j = minY; j <= maxY; j++) {
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final var value = row.getOrDefault(j, false);
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builder.append(value ? '#' : '.');
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}
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builder.append('\n');
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}
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return builder.toString();
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}
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public static Image parse(final List<String> lines) {
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final var pixels = new TreeMap<Integer, SortedMap<Integer, Boolean>>();
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final int minX = 0;
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final int minY = 0;
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int maxX = 0;
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int maxY = 0;
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for (int i = lines.size(); --i >= 0; ) {
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final var line = lines.get(i);
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final var row = new TreeMap<Integer, Boolean>();
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for (int j = line.length(); --j >= 0; ) {
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final var pixel = line.charAt(j);
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row.put(j, pixel == '#');
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if (pixel == '#') {
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row.put(j, true);
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maxY = Math.max(maxY, j);
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}
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}
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if (!row.isEmpty()) {
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maxX = Math.max(maxX, i);
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pixels.put(i, Collections.unmodifiableSortedMap(row));
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}
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}
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return new Image(Collections.unmodifiableSortedMap(pixels), minX, maxX, minY, maxY, true);
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}
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}
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@Nested
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public class ImageTest {
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@Test
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public final void testToInt() {
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final var string = """
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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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final var image = Image.parse(Arrays.asList(string.split("\n")));
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assertEquals(34, image.decode(2, 2, false));
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}
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@Test
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public final void flipAllOn() {
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final var template = "#........";
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final var imageString = """
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...
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...
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...
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""";
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final var image = Image.parse(Arrays.asList(imageString.split("\n")));
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final var result = image.enhance(ImageEnhancementAlgorithm.parse(template));
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assertTrue(result.pixels().get(1).get(1));
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}
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@Test
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public final void turnOffPixel() {
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final var templateBuilder = new StringBuilder();
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for (int i = 511; --i >= 0; templateBuilder.append('#')) ;
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templateBuilder.append('.');
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final var template = templateBuilder.toString();
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final var imageString = """
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###
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###
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###
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""";
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final var image = Image.parse(Arrays.asList(imageString.split("\n")));
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final var result = image.enhance(ImageEnhancementAlgorithm.parse(template));
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final var middleRow = result.pixels().get(1);
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assertFalse(middleRow.containsKey(1));
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}
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}
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@Test
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public final void part1() {
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final var list = getInput().toList();
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final var algorithm = ImageEnhancementAlgorithm.parse(list.get(0));
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final var image = Image.parse(list.subList(2, list.size()))
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.enhance(algorithm)
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.enhance(algorithm);
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System.out.println("Part 1: " + image.countLitPixels());
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}
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@Test
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public final void part2() {
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final var list = getInput().toList();
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final var algorithm = ImageEnhancementAlgorithm.parse(list.get(0));
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var image = Image.parse(list.subList(2, list.size()));
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for(int _i = 50; --_i >= 0; image = image.enhance(algorithm));
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System.out.println("Part 2: " + image.countLitPixels());
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}
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}

‎src/test/resources/sample/day-20.txt

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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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