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Puzzle4.java
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Puzzle4.java
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package advent2023;
import static java.nio.charset.StandardCharsets.UTF_8;
import static java.util.stream.Collectors.toSet;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* @author Éamonn McManus
*/
public class Puzzle4 {
private static final Pattern CARD_PATTERN = Pattern.compile("Card\\s+[0-9]+: (.*)\\|(.*)");
public static void main(String[] args) throws Exception {
try (InputStream in = Puzzle4.class.getResourceAsStream("puzzle4.txt")) {
String lineString = new String(in.readAllBytes(), UTF_8);
List<String> lines = List.of(lineString.split("\n"));
// Parse the input and solve Part 1.
int sum = 0;
List<Card> cards = new ArrayList<>();
for (String line : lines) {
Matcher matcher = CARD_PATTERN.matcher(line);
if (!matcher.matches()) {
throw new AssertionError(line);
}
Set<Integer> winning = parseNumbers(matcher.group(1));
Set<Integer> present = parseNumbers(matcher.group(2));
Card card = new Card(winning, present);
int count = card.score();
if (count > 0) {
sum += 1 << (count - 1);
}
cards.add(card);
}
System.out.println("Sum is " + sum);
// Part 2.
int[] counts = new int[cards.size()];
Arrays.fill(counts, 1);
for (int i = 0; i < cards.size(); i++) {
int score = cards.get(i).score();
log("Score for card " + i + 1 + " is " + score);
for (int j = 1; j <= score; j++) {
log(" Update count for " + i + j + 1 + " from " + counts[i + j] + " to " + 2 * counts[i + j]);
counts[i + j] += counts[i];
}
}
int countSum = Arrays.stream(counts).sum();
System.out.println("Count sum is " + countSum);
}
}
record Card(Set<Integer> winning, Set<Integer> present) {
int score() {
int count = 0;
for (Integer number : present) {
if (winning.contains(number)) {
count++;
}
}
return count;
}
}
private static Set<Integer> parseNumbers(String line) {
return Arrays.stream(line.split(" +")).filter(s -> !s.isEmpty()).map(Integer::parseInt).collect(toSet());
}
private static void log(String message) {
if (false) {
System.out.println(message);
}
}
}