Day 8 implementation in Java

java/src/main/java/day8/Main.java

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+package day8;
+
+import io.vavr.Tuple;
+import io.vavr.Tuple2;
+import io.vavr.collection.Iterator;
+import io.vavr.collection.List;
+import io.vavr.collection.Map;
+import util.FileReader;
+import util.MathUtils;
+
+import java.util.function.Function;
+
+public class Main {
+    enum Direction {
+        LEFT,
+        RIGHT
+    }
+
+    private static final String STARTING_NODE = "AAA";
+    private static final String ENDING_NODE = "ZZZ";
+    private static final String STARTING_NODES_SUFFIX = "A";
+    private static final String ENDING_NODES_SUFFIX = "Z";
+
+    public static void main(String[] args) {
+        String inputFilePath = System.getProperty("user.dir") + "\\java\\src\\main\\java\\day8\\input.txt";
+        FileReader reader = new FileReader(inputFilePath);
+        List<String> inputData = List.ofAll(reader.readContents());
+
+        List<Direction> instructions = List.ofAll(inputData.get(0).toCharArray())
+            .map(character -> character == 'L' ? Direction.LEFT : Direction.RIGHT);
+
+        Map<String, Tuple2<String, String>> graph = inputData.removeAt(0)
+            .filter(string -> !string.isEmpty())
+            .map(string -> string
+                .replaceAll(" ", "")
+                .replaceAll("\\(", "")
+                .replaceAll("\\)", "")
+                .replaceAll("=", ",")
+                .split(","))
+            .map(List::of)
+            .toMap(
+                nodeIds -> nodeIds.get(0),
+                nodeIds -> Tuple.of(nodeIds.get(1), nodeIds.get(2))
+            );
+
+        System.out.println(countIterationsUntilConditionIsMet(STARTING_NODE, instructions, graph, ENDING_NODE::equals));
+
+        List<Long> iterationCounts = graph.keySet().toList()
+            .filter(string -> string.endsWith(STARTING_NODES_SUFFIX))
+            .map(node -> countIterationsUntilConditionIsMet(
+                node,
+                instructions,
+                graph,
+                n -> n.endsWith(ENDING_NODES_SUFFIX)
+            ));
+
+        System.out.println(MathUtils.leastCommonMultiple(iterationCounts));
+    }
+
+    private static Long countIterationsUntilConditionIsMet(
+        String node,
+        List<Direction> instructions,
+        Map<String, Tuple2<String, String>> graph,
+        Function<String, Boolean> conditionChecker
+    ) {
+        Long count = 0L;
+        Iterator<Direction> iterator = instructions.iterator();
+        while (!conditionChecker.apply(node)) {
+            if (!iterator.hasNext()) {
+                iterator = instructions.iterator();
+            }
+            Direction direction = iterator.next();
+            node = direction == Direction.LEFT
+                ? graph.get(node).getOrElseThrow(RuntimeException::new)._1()
+                : graph.get(node).getOrElseThrow(RuntimeException::new)._2();
+            count++;
+        }
+        return count;
+    }
+}

java/src/main/java/util/MathUtils.java

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+package util;
+
+import io.vavr.collection.List;
+
+public class MathUtils {
+    public static Long leastCommonMultiple(List<Long> numbers) {
+        return numbers
+            .foldLeft(1L, (x, y) -> x * y / greaterCommonDivisor(x, y)
+        );
+    }
+
+    public static Long greaterCommonDivisor(Long number, Long other) {
+        if (other == 0) {
+            return number;
+        }
+        return greaterCommonDivisor(other,number % other);
+    }
+}