Day 9

l0s · l0s · commit bfe31dcc9514 · 2022-12-08T22:09:50.000-08:00
diff --git a/src/test/java/com/macasaet/Day09.java b/src/test/java/com/macasaet/Day09.java
@@ -0,0 +1,170 @@
+package com.macasaet;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Set;
+import java.util.SortedMap;
+import java.util.TreeMap;
+import java.util.TreeSet;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+/**
+ * --- Day 9: Rope Bridge ---
+ * <a href="https://adventofcode.com/2022/day/9">https://adventofcode.com/2022/day/9</a>
+ */
+public class Day09 {
+
+    record Coordinate(int x, int y) {
+
+        public int distance(final Coordinate other) {
+            return (int)Math.sqrt(Math.pow((double)x() - (double)other.x(), 2.0) + Math.pow((double)y() - (double)other.y(), 2.0));
+        }
+
+        public Coordinate step(final int xDistance, final int yDistance) {
+            return new Coordinate(x() + xDistance, y + yDistance);
+        }
+        public Coordinate stepTowards(final Coordinate leader) {
+            final var xDistance = Integer.compare(leader.x(), x());
+            final var yDistance = Integer.compare(leader.y(), y());
+            return step(xDistance, yDistance);
+        }
+    }
+
+    public static class Rope {
+
+        Coordinate[] knotCoordinates;
+
+        final SortedMap<Integer, Set<Integer>> visited = new TreeMap<>();
+
+        public Rope(final int knots) {
+            knotCoordinates = new Coordinate[knots];
+            for(int i = knots; --i >= 0; knotCoordinates[i] = new Coordinate(0, 0));
+            visited.computeIfAbsent(0, (key) -> new TreeSet<>()).add(0);
+        }
+
+        public int countVisited() {
+            int result = 0;
+            for( final var map : visited.values() ) {
+                result += map.size();
+            }
+            return result;
+        }
+
+        public void process(final Instruction instruction) {
+            final int xStep = instruction.direction().xStep();
+            final int yStep = instruction.direction().yStep();
+
+            for(int i = instruction.distance(); --i >= 0; ) {
+                knotCoordinates[0] = knotCoordinates[0].step(xStep, yStep);
+                for(int j = 1; j < knotCoordinates.length; j++) {
+                    moveKnot(j);
+                }
+            }
+        }
+
+        protected void moveKnot(int knotIndex) {
+            if(knotIndex <= 0) {
+                throw new IllegalArgumentException("Cannot move head");
+            }
+            final var leader = knotCoordinates[knotIndex - 1];
+            var follower = knotCoordinates[knotIndex];
+
+            if(leader.equals(follower)) {
+                return;
+            } else if (leader.distance(follower) <= 1) {
+                return;
+            }
+
+            follower = follower.stepTowards(leader);
+            knotCoordinates[knotIndex] = follower;
+
+            if(knotIndex == knotCoordinates.length - 1) {
+                visited.computeIfAbsent(follower.x(), (key) -> new TreeSet<>()).add(follower.y());
+            }
+        }
+
+    }
+
+    enum Direction {
+        Up {
+            int xStep() {
+                return -1;
+            }
+            int yStep() {
+                return 0;
+            }
+        },
+        Down {
+            int xStep() {
+                return 1;
+            }
+            int yStep() {
+                return 0;
+            }
+        },
+        Left {
+            int xStep() {
+                return 0;
+            }
+            int yStep() {
+                return -1;
+            }
+        },
+        Right {
+            int xStep() {
+                return 0;
+            }
+            int yStep() {
+                return 1;
+            }
+        };
+
+        abstract int xStep();
+        abstract int yStep();
+
+        static Direction parse(final String string) {
+            return switch(string.trim()) {
+                case "U" -> Up;
+                case "D" -> Down;
+                case "L" -> Left;
+                case "R" -> Right;
+                default -> throw new IllegalArgumentException("Invalid direction: " + string);
+            };
+        }
+    }
+
+    record Instruction(Direction direction, int distance) {
+        static Instruction parse(final String string) {
+            final var components = string.split(" ");
+            final var direction = Direction.parse(components[0]);
+            final var distance = Integer.parseInt(components[1]);
+            return new Instruction(direction, distance);
+        }
+    }
+
+    protected Stream<Instruction> getInput() {
+        return StreamSupport
+                .stream(new LineSpliterator("day-09.txt"),
+                        false)
+                .map(Instruction::parse);
+    }
+
+    @Test
+    public final void part1() {
+        final var rope = new Rope(2);
+        getInput().forEach(rope::process);
+        final var result = rope.countVisited();
+        System.out.println("Part 1: " + result);
+        // NOT 7017
+    }
+
+    @Test
+    public final void part2() {
+        final var rope = new Rope(10);
+        getInput().forEach(rope::process);
+        final var result = rope.countVisited();
+        System.out.println("Part 2: " + result);
+    }
+
+}
diff --git a/src/test/resources/sample/day-09.txt b/src/test/resources/sample/day-09.txt
@@ -0,0 +1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2

-Original file line number
+Diff line change
@@ @@ -0,0 +1,8 @@ @@
 +R 4
 +U 4
 +L 3
 +D 1
 +R 4
 +D 1
 +L 5
 +R 2