Add day 20 solution

Author: SvenWoltmann

src/main/java/eu/happycoders/adventofcode2022/day20/Day20Solver.java

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+package eu.happycoders.adventofcode2022.day20;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Advent of Code 2022 – Object-Oriented Solutions in Java.
+ *
+ * <p>Puzzle solver for day 20.
+ *
+ * @author <a href="mailto:sven@happycoders.eu">Sven Woltmann</a>
+ */
+class Day20Solver {
+
+  private static final long DECRYPTION_KEY = 811_589_153L;
+
+  static long solveTask1(String input) {
+    List<Long> numbers = ListParser.parse(input);
+    File file = new File(numbers);
+    file.mix();
+    return file.getGroveCoordinates();
+  }
+
+  static long solveTask2(String input) {
+    List<Long> numbers = new ArrayList<>(ListParser.parse(input));
+
+    numbers.replaceAll(value -> value * DECRYPTION_KEY);
+
+    File file = new File(numbers);
+    for (int i = 0; i < 10; i++) {
+      file.mix();
+    }
+    return file.getGroveCoordinates();
+  }
+}

src/main/java/eu/happycoders/adventofcode2022/day20/File.java

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+package eu.happycoders.adventofcode2022.day20;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Advent of Code 2022 – Object-Oriented Solutions in Java.
+ *
+ * <p>The file to be decrypted.
+ *
+ * @author <a href="mailto:sven@happycoders.eu">Sven Woltmann</a>
+ */
+class File {
+
+  private final List<Node> nodesInOriginalOrder = new ArrayList<>();
+  private final int size;
+  private final Node zeroNode;
+
+  File(List<Long> numbers) {
+    size = numbers.size();
+
+    // Store all numbers in a doubly-linked list.
+    // And remember the original order of the nodes and the zero node.
+    Node tempZeroNode = null;
+    for (int i = 0; i < size; i++) {
+      Long number = numbers.get(i);
+      Node node = new Node(number);
+
+      nodesInOriginalOrder.add(node);
+
+      if (number == 0) {
+        tempZeroNode = node;
+      }
+
+      if (i > 0) {
+        Node previousNode = nodesInOriginalOrder.get(i - 1);
+        previousNode.setNext(node);
+        node.setPrevious(previousNode);
+      }
+    }
+
+    this.zeroNode = tempZeroNode;
+
+    // Make the list circular
+    Node firstNode = nodesInOriginalOrder.get(0);
+    Node lastNode = nodesInOriginalOrder.get(size - 1);
+    firstNode.setPrevious(lastNode);
+    lastNode.setNext(firstNode);
+  }
+
+  void mix() {
+    for (int i = 0; i < size; i++) {
+      Node node = nodesInOriginalOrder.get(i);
+      move(node);
+    }
+  }
+
+  private void move(Node node) {
+    long distance = node.value() % (size - 1);
+    if (distance == 0) {
+      return;
+    }
+
+    Node previous = node.previous();
+    Node next = node.next();
+
+    // Remove node from current position
+    previous.setNext(next);
+    next.setPrevious(previous);
+
+    if (distance < 0) {
+      for (long i = 0; i > distance; i--) {
+        next = previous;
+        previous = previous.previous();
+      }
+    } else {
+      for (long i = 0; i < distance; i++) {
+        previous = next;
+        next = next.next();
+      }
+    }
+
+    // Insert node at new position
+    previous.setNext(node);
+    node.setPrevious(previous);
+    node.setNext(next);
+    next.setPrevious(node);
+  }
+
+  long getGroveCoordinates() {
+    Node node = zeroNode;
+
+    long sum = 0;
+    for (int i = 0; i < 3; i++) {
+      node = skipNodes(node, 1000);
+      sum += node.value();
+    }
+
+    return sum;
+  }
+
+  private Node skipNodes(Node node, int numberOfNodes) {
+    int remainder = numberOfNodes % size;
+    for (int i = 0; i < remainder; i++) {
+      node = node.next();
+    }
+    return node;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder result = new StringBuilder();
+    Node node = nodesInOriginalOrder.get(0);
+    for (int i = 0; i < size; i++) {
+      if (result.length() > 0) {
+        result.append(", ");
+      }
+      result.append(node.value());
+      node = node.next();
+    }
+    return result.toString();
+  }
+}

src/main/java/eu/happycoders/adventofcode2022/day20/ListParser.java

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+package eu.happycoders.adventofcode2022.day20;
+
+import java.util.List;
+
+/**
+ * Advent of Code 2022 – Object-Oriented Solutions in Java.
+ *
+ * <p>Parses the input into a list of Longs.
+ *
+ * @author <a href="mailto:sven@happycoders.eu">Sven Woltmann</a>
+ */
+class ListParser {
+
+  static List<Long> parse(String input) {
+    return input.lines().map(Long::parseLong).toList();
+  }
+}