Day 4 implementation in Java

java/src/main/java/day4/Card.java

@@ -0,0 +1,39 @@
+package day4;
+
+import io.vavr.collection.List;
+import lombok.Getter;
+
+public class Card {
+    private static final String CARD_ID_SEPARATOR = ":";
+    private static final String CARD_NUMBERS_SEPARATOR = "\\|";
+    private static final String CARD_ID_PREFIX = "Card";
+
+    @Getter
+    private final Integer id;
+    private final List<Integer> winningNumbers;
+    private final List<Integer> cardNumbers;
+    public Card(String cardRepresentation) {
+        String[] splitCardRepresentation = cardRepresentation.split(CARD_ID_SEPARATOR, 2);
+        this.id = Integer.parseInt(splitCardRepresentation[0].replace(CARD_ID_PREFIX, "").replaceAll(" ", ""));
+
+        String[] splitNumbers = splitCardRepresentation[1].split(CARD_NUMBERS_SEPARATOR, 2);
+        this.winningNumbers = convertStringToListOfNumbers(splitNumbers[0]);
+        this.cardNumbers = convertStringToListOfNumbers(splitNumbers[1]);
+    }
+
+    private List<Integer> convertStringToListOfNumbers(String inputString) {
+        return List.of(inputString.split(" "))
+            .filter(string -> !string.isEmpty())
+            .map(string -> string.replaceAll(" ", ""))
+            .map(Integer::parseInt);
+    }
+
+    public Integer getNumberOfMatches() {
+        return cardNumbers.filter(winningNumbers::contains).length();
+    }
+
+    public Integer getScore() {
+        Integer numberOfMatches = getNumberOfMatches();
+        return numberOfMatches == 0 ? 0 : (new Double(Math.pow(2, numberOfMatches - 1))).intValue();
+    }
+}

java/src/main/java/day4/Main.java

@@ -0,0 +1,31 @@
+package day4;
+
+import io.vavr.collection.List;
+import util.FileReader;
+
+import java.util.HashMap;
+
+public class Main {
+    public static void main(String[] args) {
+        String inputFilePath = System.getProperty("user.dir") + "\\java\\src\\main\\java\\day4\\input.txt";
+        FileReader reader = new FileReader(inputFilePath);
+        List<String> inputData = List.ofAll(reader.readContents());
+
+        List<Card> cards = inputData.map(Card::new);
+        System.out.println(cards.map(Card::getScore).reduce(Integer::sum));
+
+        HashMap<Card, Integer> cardsCount = new HashMap<>();
+        cards.forEach(card -> cardsCount.put(card, 1));
+        cards.forEach(card -> {
+            Integer matches = card.getNumberOfMatches();
+            Integer numberOfCards = cardsCount.get(card);
+            for (Integer index = card.getId(); index < card.getId() + matches; index++) {
+                Card currentCard = cards.get(index);
+                cardsCount.put(currentCard, cardsCount.get(currentCard) + numberOfCards);
+            }
+        });
+
+        Integer numberOfCards = cardsCount.values().stream().reduce(Integer::sum).orElse(0);
+        System.out.println(numberOfCards);
+    }
+}