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l0sl0s
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Days 1 through 20
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‎.gitignore

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.classpath
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.idea
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.project
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.settings
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advent-of-code.iml
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target/

‎pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.macasaet</groupId>
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<artifactId>advent-of-code</artifactId>
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<version>0.2020.0-SNAPSHOT</version>
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<name>Advent of Code 2020</name>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<maven.compiler.source>14</maven.compiler.source>
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<maven.compiler.target>14</maven.compiler.target>
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</properties>
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</project>

‎src/test/java/com/macasaet/Day01.java

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package com.macasaet;
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Spliterator;
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import java.util.stream.StreamSupport;
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public class Day01 {
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public static void main(String[] args) throws IOException {
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try( var spliterator = new LineSpliterator(Day01.class.getResourceAsStream("/day-1-input.txt")) ) {
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// part1(spliterator);
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part2(spliterator);
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}
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}
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protected static void part1(final Spliterator<String> spliterator) {
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final var items = StreamSupport.stream(spliterator, false)
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.mapToInt(Integer::parseInt)
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.filter(candidate -> candidate <= 2020) // filter out the obvious
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.sorted() // sort to ensure the complement is to the left
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.collect(ArrayList<Integer>::new, List::add, List::addAll);
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for( int i = items.size(); --i >= 0; ) {
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final int x = items.get(i);
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for( int j = i; --j >= 0; ) { // avoid retrying combinations
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final int y = items.get(j);
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if( x + y == 2020 ) {
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System.out.println( "" + ( x * y ) );
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return;
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}
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}
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}
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}
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protected static void part2(final Spliterator<String> spliterator) {
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final var items = StreamSupport.stream(spliterator, false)
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.mapToInt(Integer::parseInt)
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.filter(candidate -> candidate <= 2020) // filter out the obvious
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.sorted() // sort to ensure the complements are to the left
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.collect(ArrayList<Integer>::new, List::add, List::addAll);
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for( int i = items.size(); --i >= 0; ) {
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final int x = items.get(i);
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for( int j = i; --j >= 0; ) {
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final int y = items.get(j);
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for( int k = j; --k >= 0; ) {
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final int z = items.get(k);
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if( x + y + z == 2020 ) {
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System.out.println( "" + ( x * y * z ) );
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return;
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}
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}
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}
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}
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}
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}

‎src/test/java/com/macasaet/Day02.java

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package com.macasaet;
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import java.io.IOException;
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import java.util.regex.Pattern;
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import java.util.stream.StreamSupport;
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public class Day02 {
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public static void main(String[] args) throws IOException {
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try( var spliterator = new LineSpliterator( Day02.class.getResourceAsStream("/day-2-input.txt" ) ) ) {
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final long count = StreamSupport.stream(spliterator, false)
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// .map(SledEntry::build) // part 1
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.map(TobogganEntry::build) // part 2
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.filter(Entry::isValid).count();
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System.out.println("" + count);
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}
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}
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public static abstract class Entry {
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// TODO consider a more robust pattern:
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// https://stackoverflow.com/a/4731164/914887
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protected static final Pattern separator = Pattern.compile("\\s");
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protected static final Pattern rangeSeparator = Pattern.compile("-");
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protected final char c; // TODO support code points
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protected final String password;
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protected Entry(final char c, final String password) {
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this.c = c;
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this.password = password;
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}
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public abstract boolean isValid();
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}
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public static class SledEntry extends Entry {
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private final long minIterations;
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private final long maxIterations;
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public SledEntry( final char c, final String password, final long minIterations, final long maxIterations ) {
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super(c, password);
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this.minIterations = minIterations;
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this.maxIterations = maxIterations;
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}
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public static Entry build(final String line) {
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final var components = separator.split(line, 3);
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final var range = components[0];
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final var rangeComponents = rangeSeparator.split(range, 2);
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return new SledEntry(components[1].charAt(0),
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components[2],
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Long.parseLong(rangeComponents[ 0 ]),
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Long.parseLong(rangeComponents[ 1 ] ));
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}
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public boolean isValid() {
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final var count = password.chars()
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.filter(candidate -> (char) candidate == this.c)
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.count();
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return count >= minIterations && count <= maxIterations;
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}
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}
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public static class TobogganEntry extends Entry {
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private final int firstPosition;
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private final int secondPosition;
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public TobogganEntry( final char c, final String password, final int firstPosition, final int secondPosition ) {
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super( c, password );
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this.firstPosition = firstPosition;
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this.secondPosition = secondPosition;
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}
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public static Entry build( final String line ) {
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final var components = separator.split( line, 3 );
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final var positionComponents = rangeSeparator.split( components[ 0 ], 2 );
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return new TobogganEntry( components[ 1 ].charAt( 0 ),
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components[ 2 ],
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Integer.parseInt( positionComponents[ 0 ] ),
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Integer.parseInt( positionComponents[ 1 ] ) );
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}
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public boolean isValid() {
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final var x = password.charAt(firstPosition - 1);
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final var y = password.charAt(secondPosition - 1);
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return x == c ^ y == c;
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}
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}
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}

‎src/test/java/com/macasaet/Day03.java

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package com.macasaet;
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import java.io.IOException;
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import java.math.BigInteger;
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import java.util.Arrays;
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import java.util.stream.Collectors;
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import java.util.stream.StreamSupport;
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public class Day03 {
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public static void main(String[] args) throws IOException {
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try( var spliterator = new LineSpliterator( Day03.class.getResourceAsStream("/day-3-input.txt" ) ) ) {
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final var rowList = StreamSupport.stream(spliterator, false)
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.map(String::toCharArray)
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.collect(Collectors.toUnmodifiableList());
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final var matrix = new char[rowList.size()][];
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for (int i = rowList.size(); --i >= 0; matrix[i] = rowList.get(i));
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final var slopes = new int[][] {
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new int[] { 1, 1 },
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new int[] { 3, 1 }, // uncomment all but this for "part 1"
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new int[] { 5, 1 },
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new int[] { 7, 1 },
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new int[] { 1, 2 },
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};
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final var totalTrees = Arrays.stream(slopes)
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.mapToLong(pair -> {
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final int slopeRight = pair[0];
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final int slopeDown = pair[1];
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long numTrees = 0;
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int rowIndex = 0;
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int columnIndex = 0;
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do {
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final var row = matrix[rowIndex];
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final var cell = row[columnIndex];
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if (cell == '#') {
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numTrees += 1l;
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}
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rowIndex += slopeDown;
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columnIndex = columnIndex + slopeRight;
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columnIndex = columnIndex % row.length; // "These aren't the only trees, though; due to
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// something you read about once involving
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// arboreal genetics and biome stability, the
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// same pattern repeats to the right many times"
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} while( rowIndex < matrix.length );
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return numTrees;
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}).mapToObj(BigInteger::valueOf) // I wasn't sure how large these (multiplied) values could get, in retrospect, `long` would have been fine
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.reduce(BigInteger::multiply)
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.get();
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System.out.println("" + totalTrees.toString());
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}
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}
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}

‎src/test/java/com/macasaet/Day04.java

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package com.macasaet;
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.Set;
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import java.util.stream.Collectors;
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import java.util.stream.StreamSupport;
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public class Day04 {
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public static void main(String[] args) throws IOException {
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try (var spliterator = new LineSpliterator( Day04.class.getResourceAsStream( "/day-4-input.txt" ) ) ) {
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final var rawLines = StreamSupport.stream(spliterator, false)
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.collect(Collectors.toUnmodifiableList());
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String current = "";
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// collect all the text blocks into entries (separated by empty lines)
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final var entries = new ArrayList<String>();
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for (final var line : rawLines) {
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if (line.isBlank()) {
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if (!current.isBlank()) {
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entries.add(current);
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current = "";
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}
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} else {
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current += " " + line;
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}
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}
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if (!current.isBlank()) {
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entries.add(current);
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}
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int numValid = 0;
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for (final var entry : entries) {
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final var pairs = entry.split("\\s");
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final var map = new HashMap<String, String>();
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for (final var pair : pairs) {
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if (pair.isBlank()) {
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continue;
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}
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final var components = pair.split(":", 2);
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map.put(components[0].trim(), components[1].trim());
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}
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final var birthYearString = map.get("byr");
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final var issueYearString = map.get("iyr");
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final var expirationYearString = map.get("eyr");
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final var heightString = map.get("hgt");
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final var hairColour = map.get("hcl");
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final var eyeColour = map.get("ecl");
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final var validEyeColours = Set.of("amb", "blu", "brn", "gry", "grn", "hzl", "oth");
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final var passportId = map.get("pid");
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if (birthYearString == null) continue;
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final int birthYear = Integer.parseInt(birthYearString);
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if (birthYear < 1920 || birthYear > 2002) continue;
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if (issueYearString == null) continue;
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final int issueYear = Integer.parseInt(issueYearString);
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if (issueYear < 2010 || issueYear > 2020) continue;
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if (expirationYearString == null) continue;
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final int expirationYear = Integer.parseInt(expirationYearString);
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if (expirationYear < 2020 || expirationYear > 2030) continue;
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if (heightString == null) continue;
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if (heightString.endsWith("cm")) {
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final int centimetres = Integer.parseInt(heightString.replace("cm", ""));
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if (centimetres < 150 || centimetres > 193) continue;
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} else if (heightString.endsWith("in")) {
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final int inches = Integer.parseInt(heightString.replace("in", ""));
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if (inches < 59 || inches > 76) continue;
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} else {
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continue;
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}
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if (hairColour == null) continue;
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if (!hairColour.matches("#[0-9a-f]{6}")) continue;
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if (eyeColour == null) continue;
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if (!validEyeColours.contains(eyeColour)) continue;
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if (passportId == null) continue;
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if (!passportId.matches("[0-9]{9}")) continue;
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numValid++;
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}
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System.out.println(numValid);
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}
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}
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}

‎src/test/java/com/macasaet/Day05.java

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package com.macasaet;
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import java.io.IOException;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.stream.StreamSupport;
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public class Day05 {
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public static void main(String[] args) throws IOException {
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try (var spliterator = new LineSpliterator( Day05.class.getResourceAsStream( "/day-5-input.txt" ) ) ) {
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final var seatIds = StreamSupport.stream(spliterator, false)
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.mapToInt(id -> {
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int maxRowExclusive = 128;
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int row = 0;
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for( int i = 0; i < 7; i++ ) {
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final char partition = id.charAt(i);
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if( partition == 'B' ) {
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row = ( ( maxRowExclusive - row ) / 2 ) + row;
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} else if( partition == 'F' ) {
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maxRowExclusive = maxRowExclusive - ( ( maxRowExclusive - row ) / 2 );
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} else {
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throw new IllegalArgumentException("Invalid row partition: " + partition);
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}
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}
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int column = 0;
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int maxColumnExclusive = 8;
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for( int i = 7; i < 10; i++ ) {
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final char half = id.charAt(i);
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if( half == 'R' ) {
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column = ( ( maxColumnExclusive - column ) / 2 ) + column;
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} else if( half == 'L' ) {
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maxColumnExclusive = maxColumnExclusive - ( ( maxColumnExclusive - column ) / 2 );
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} else {
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throw new IllegalArgumentException("Invalid column partition: " + half);
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}
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}
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final int seatId = row * 8 + column;
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return seatId;
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})
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.sorted()
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.collect(ArrayList<Integer>::new, List::add, List::addAll);
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System.out.println("part 1: " + seatIds.get(seatIds.size() - 1));
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for( int i = seatIds.size(); --i >= 1; ) {
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final int x = seatIds.get( i - 1 );
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final int y = seatIds.get( i );
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if( y - x > 1 ) {
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System.out.println("part 2: " + ( x + 1 ) );
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return;
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}
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}
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}
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}
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}

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