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Day 8
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‎src/test/java/com/macasaet/Day08.java

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package com.macasaet;
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import java.util.*;
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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 8: Seven Segment Search ---
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*/
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public class Day08 {
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protected Stream<String> getInput() {
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return StreamSupport
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.stream(new LineSpliterator("day-08.txt"),
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false);
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}
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public record Digit(List<Character> segments) {
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public Digit decode(final Map<Character, Character> map) {
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return new Digit(segments().stream()
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.map(map::get)
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.collect(Collectors.toUnmodifiableList()));
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}
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public int asInt() {
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if (segments().size() == 6 && hasSegments('a', 'b', 'c', 'e', 'f', 'g')) { // FIXME use on/off mechanism
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return 0;
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} else if (segments().size() == 2 && hasSegments('c', 'f')) {
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return 1;
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} else if (segments().size() == 5 && hasSegments('a', 'c', 'd', 'e', 'g')) {
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return 2;
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} else if (segments().size() == 5 && hasSegments('a', 'c', 'd', 'f', 'g')) {
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return 3;
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} else if (segments().size() == 4 && hasSegments('b', 'c', 'd', 'f')) {
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return 4;
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} else if (segments().size() == 5 && hasSegments('a', 'b', 'd', 'f', 'g')) {
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return 5;
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} else if (segments().size() == 6 && hasSegments('a', 'b', 'd', 'e', 'f', 'g')) {
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return 6;
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} else if (segments().size() == 3 && hasSegments('a', 'c', 'f')) {
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return 7;
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} else if (segments().size() == 7 && hasSegments('a', 'b', 'c', 'd', 'e', 'f', 'g')) {
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return 8;
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} else if (segments().size() == 6 && hasSegments('a', 'b', 'c', 'd', 'f', 'g')) {
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return 9;
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}
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throw new IllegalStateException("Invalid Digit: " + this);
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}
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public boolean hasSegments(final char... segments) {
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for (final var segment : segments) {
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if (!hasSegment(segment)) {
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return false;
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}
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}
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return true;
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}
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public boolean hasSegment(final char segment) {
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return segments().contains(segment);
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}
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public static Digit parse(final String string) {
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final var array = string.toCharArray();
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final var list = new ArrayList<Character>(array.length);
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for (final var c : array) {
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list.add(c);
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}
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return new Digit(Collections.unmodifiableList(list));
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}
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}
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public static record Entry(List<Digit> uniqueSignalPatterns, List<Digit> outputValue) {
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public int decodeOutput() {
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final var map = buildDecodingMap();
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final StringBuilder builder = new StringBuilder();
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for (final var outputDigit : outputValue()) {
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final var decodedDigit = outputDigit.decode(map);
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final int digit = decodedDigit.asInt();
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builder.append(digit);
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}
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final String stringInt = builder.toString();
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return Integer.parseInt(stringInt);
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}
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protected SortedSet<Character> getDigitSegmentsWithCount(final int n) {
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return uniqueSignalPatterns().stream()
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.filter(digit -> digit.segments().size() == n)
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.findFirst()
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.get()
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.segments()
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.stream()
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.collect(TreeSet::new, SortedSet::add, SortedSet::addAll);
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}
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protected Set<Digit> getDigitsWithCount(final int n) { // TODO return stream
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return uniqueSignalPatterns()
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.stream()
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.filter(digit -> digit.segments().size() == n).collect(Collectors.toUnmodifiableSet());
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}
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public Map<Character, Character> buildDecodingMap() {
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final var encodingMap = buildEncodingMap();
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final var result = new HashMap<Character, Character>();
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for(final var entry : encodingMap.entrySet()) {
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result.put(entry.getValue(), entry.getKey());
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}
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return Collections.unmodifiableMap(result);
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}
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public Map<Character, Character> buildEncodingMap() {
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final var map = new HashMap<Character, Character>();
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final var oneSegments = getDigitSegmentsWithCount(2);
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final var sevenSegments = getDigitSegmentsWithCount(3);
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final var fourSegments = getDigitSegmentsWithCount(4);
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final var eightSegments = getDigitSegmentsWithCount(7);
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final var aMapping = sevenSegments.stream().filter(c -> !oneSegments.contains(c)).findFirst().get();
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map.put('a', aMapping);
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final var zeroSixNine = getDigitsWithCount(6);
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var zsnSegments = zeroSixNine.stream().flatMap(digit -> digit.segments().stream()).collect(Collectors.toList());
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zsnSegments.removeIf(sevenSegments::contains);
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zsnSegments.removeIf(fourSegments::contains);
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final var sssMap = new HashMap<Character, Integer>();
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for (final var c : zsnSegments) {
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sssMap.compute(c, (_key, old) -> old == null ? 1 : old + 1);
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}
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if(sssMap.size() != 2) {
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throw new IllegalStateException("More segments for 0, 6, 9 encountered: " + sssMap);
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}
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for (final var entry : sssMap.entrySet()) {
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if (entry.getValue() == 3) {
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map.put('g', entry.getKey());
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} else if (entry.getValue() == 2) {
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map.put('e', entry.getKey());
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} else {
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throw new IllegalStateException();
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}
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}
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final var twoFiveThree = getDigitsWithCount(5);
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var tftSegments = twoFiveThree.stream().flatMap(digit -> digit.segments.stream()).collect(Collectors.toList());
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tftSegments.removeIf(sevenSegments::contains);
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tftSegments.removeIf(candidate -> candidate.equals(map.get('e')));
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tftSegments.removeIf(candidate -> candidate.equals(map.get('g')));
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final var tftCounts = new HashMap<Character, Integer>();
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for(final var c : tftSegments) {
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tftCounts.compute(c, (_key, old) -> old == null ? 1 : old + 1);
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}
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for(final var entry : tftCounts.entrySet()) {
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if(entry.getValue() == 3) {
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map.put('d', entry.getKey());
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} else if(entry.getValue() == 1) {
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map.put('b', entry.getKey());
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} else {
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throw new IllegalStateException();
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}
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}
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zsnSegments = zeroSixNine.stream().flatMap(digit -> digit.segments().stream()).collect(Collectors.toList());
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zsnSegments.removeIf(candidate -> candidate.equals(map.get('a')));
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zsnSegments.removeIf(candidate -> candidate.equals(map.get('b')));
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zsnSegments.removeIf(candidate -> candidate.equals(map.get('d')));
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zsnSegments.removeIf(candidate -> candidate.equals(map.get('e')));
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zsnSegments.removeIf(candidate -> candidate.equals(map.get('g')));
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final var zsnCounts = new HashMap<Character, Integer>();
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for(final var c : zsnSegments) {
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zsnCounts.compute(c, (_key, old) -> old == null ? 1 : old + 1);
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}
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for(final var entry : zsnCounts.entrySet()) {
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if(entry.getValue() == 2) {
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map.put('c', entry.getKey());
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} else if( entry.getValue() == 3) {
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map.put('f', entry.getKey());
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} else {
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throw new IllegalStateException();
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}
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}
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return map;
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}
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public static Entry parse(final String string) {
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final var components = string.split(" \\| ");
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final var uniqueSignalPatterns = components[0].split(" ");
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final var outputValue = components[1].split(" ");
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return new Entry(Arrays.stream(uniqueSignalPatterns)
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.map(Digit::parse)
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.collect(Collectors.toUnmodifiableList()),
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Arrays.stream(outputValue)
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.map(Digit::parse)
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.collect(Collectors.toUnmodifiableList()));
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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 result = getInput()
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.map(Entry::parse)
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.flatMap(entry -> entry.outputValue().stream())
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.filter(digit -> {
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final var segments = digit.segments();
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final var numSegments = segments.size();
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return numSegments == 2 || numSegments == 4 || numSegments == 3 || numSegments == 7;
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})
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.count();
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System.out.println("Part 1: " + result);
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}
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@Test
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public final void part2() {
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final var result = getInput()
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.map(Entry::parse)
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.mapToInt(Entry::decodeOutput).sum();
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System.out.println("Part 2: " + result);
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}
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}

‎src/test/resources/sample/day-08.txt

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be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb | fdgacbe cefdb cefbgd gcbe
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edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec | fcgedb cgb dgebacf gc
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fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef | cg cg fdcagb cbg
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fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega | efabcd cedba gadfec cb
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aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga | gecf egdcabf bgf bfgea
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fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf | gebdcfa ecba ca fadegcb
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dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf | cefg dcbef fcge gbcadfe
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bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd | ed bcgafe cdgba cbgef
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egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg | gbdfcae bgc cg cgb
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gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc | fgae cfgab fg bagce

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