8000 Day 5 · l0s/advent-of-code-java@7c8ccb9 · GitHub
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Day 5
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‎src/test/java/com/macasaet/Day05.java

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package com.macasaet;
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import java.util.function.Predicate;
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import java.util.stream.Collectors;
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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.Test;
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/**
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* --- Day 5: Hydrothermal Venture ---
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*/
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public class Day05 {
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/**
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* A point on the ocean floor
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*/
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public static record Point(int x, int y) {
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public static Point parse(final String string) {
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final var components = string.split(",");
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return new Point(Integer.parseInt(components[0]), Integer.parseInt(components[1]));
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}
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}
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/**
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* A portion of the ocean floor on which there are hydrothermal vents, which produce large, opaque clouds
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*/
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public static record LineSegment(Point start, Point end) {
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public static LineSegment parse(final String string) {
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final var components = string.split(" -> ");
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return new LineSegment(Point.parse(components[0]), Point.parse(components[1]));
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}
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/**
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* Highlight the location of this line segment on the diagram. Each cell that this segment covers will have its
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* value incremented. The higher the number, the more vents cover the cell.
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*
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* @param diagram A map of the ocean floor which will be updated by this call.
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*/
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public void update(final int[][] diagram) {
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/*
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"Because of the limits of the hydrothermal vent mapping system, the lines in your list will only ever be
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horizontal, vertical, or a diagonal line at exactly 45 degrees."
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*/
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final int horizontalStep = start().x() == end().x()
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? 0
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: start().x() < end().x()
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? 1
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: -1;
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final int verticalStep = start().y() == end().y()
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? 0
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: start().y() < end().y()
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? 1
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: -1;
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final Predicate<Integer> xTester = start().x() == end().x()
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? x -> true
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: start().x() < end().x()
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? x -> x <= end().x()
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: x -> x >= end().x();
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final Predicate<Integer> yTester = start().y() == end().y()
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? y -> true
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: start().y() < end().y()
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? y -> y <= end().y()
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: y -> y >= end().y();
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for (int i = start().x(), j = start().y();
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xTester.test(i) && yTester.test(j);
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i += horizontalStep, j += verticalStep) {
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diagram[i][j]++;
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}
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}
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public int lowestX() {
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return Math.min(start().x(), end().x());
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}
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public int highestX() {
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return Math.max(start().x(), end().x());
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}
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public int lowestY() {
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return Math.min(start().y(), end().y());
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}
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public int highestY() {
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return Math.max(start().y(), end().y());
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}
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public String toString() {
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return start() + " -> " + end();
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}
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}
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protected Stream<LineSegment> getInput() {
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return StreamSupport
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.stream(new LineSpliterator("day-05.txt"),
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false)
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.map(LineSegment::parse);
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}
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protected record Extremes(int lowestX, int lowestY, int highestX, int highestY) {
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public Extremes combine(final LineSegment segment) {
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return new Extremes(Math.min(lowestX(), segment.lowestX()),
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Math.min(lowestY(), segment.lowestY()),
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Math.max(highestX(), segment.highestX()),
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Math.max(highestY(), segment.highestY()));
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}
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public Extremes combine(final Extremes other) {
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return new Extremes(Math.min(lowestX(), other.lowestX()),
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Math.min(lowestY(), other.lowestY()),
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Math.max(highestX(), other.highestX()),
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Math.max(highestY(), other.highestY()));
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}
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public int[][] createBlankDiagram() {
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final int[][] result = new int[highestX() + 1][];
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for (int i = result.length; --i >= 0; result[i] = new int[highestY() + 1]) ;
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return result;
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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 segments = getInput()
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// "For now, only consider horizontal and vertical lines: lines where either x1 = x2 or y1 = y2."
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.filter(segment -> segment.start().x() == segment.end().x() || segment.start().y() == segment.end().y())
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.collect(Collectors.toList());
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final var extremes = segments
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.stream()
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.reduce(new Extremes(0, 0, 0, 0),
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Extremes::combine,
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Extremes::combine);
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// there are no negative values
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// Note, we could save a little bit of space and time by using a smaller map since none of the line segments
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// need point 0,0. However, the savings are likely negligible.
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final int[][] diagram = extremes.createBlankDiagram();
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for (final var segment : segments) {
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segment.update(diagram);
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}
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int sum = 0;
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for (int i = diagram.length; --i >= 0; ) {
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final var row = diagram[i];
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for (int j = row.length; --j >= 0; ) {
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if (row[j] >= 2) {
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sum++;
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}
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}
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}
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System.out.println("Part 1: " + sum);
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}
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@Test
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public final void part2() {
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/*
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"Unfortunately, considering only horizontal and vertical lines doesn't give you the full picture; you need to
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also consider diagonal lines."
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*/
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final var segments = getInput()
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.collect(Collectors.toList());
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final var extremes = segments
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.stream()
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.reduce(new Extremes(0, 0, 0, 0),
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Extremes::combine,
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Extremes::combine);
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// there are no negative values
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// Note, we could save a little bit of space and time by using a smaller map since none of the line segments
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// need point 0,0. However, the savings are likely negligible.
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final int[][] diagram = extremes.createBlankDiagram();
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for (final var segment : segments) {
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segment.update(diagram);
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}
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int sum = 0;
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for (int i = diagram.length; --i >= 0; ) {
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final var row = diagram[i];
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for (int j = row.length; --j >= 0; ) {
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if (row[j] >= 2) {
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sum++;
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}
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}
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}
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System.out.println("Part 2: " + sum);
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}
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}

‎src/test/resources/sample/day-05.txt

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0,9 -> 5,9
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8,0 -> 0,8
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9,4 -> 3,4
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2,2 -> 2,1
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7,0 -> 7,4
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6,4 -> 2,0
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0,9 -> 2,9
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3,4 -> 1,4
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0,0 -> 8,8
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5,5 -> 8,2

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