aoc 2024 day 16

adventofcode/README.md

@@ -1454,7 +1454,7 @@
 [20232402tests]: src/test/java/org/ck/adventofcode/year2023/Day24Test.java
 [20232501tests]: src/test/java/org/ck/adventofcode/year2023/Day25Test.java
 
-# 2024 (30/49)
+# 2024 (32/49)
 
 |        # | Name                                              | Solution                             | Test                              |
 |---------:|---------------------------------------------------|:------------------------------------:|:---------------------------------:|
@@ -1488,8 +1488,8 @@
 | 20241402 | [Day 14: Restroom Redoubt - Part 2][20241402]     | ✅[💾][20241402solution] | ✅[💾][20241402tests] |
 | 20241501 | [Day 15: Warehouse Woes][20241501]                | ✅[💾][20241501solution] | ✅[💾][20241501tests] |
 | 20241502 | [Day 15: Warehouse Woes - Part 2][20241502]       | ✅[💾][20241502solution] | ✅[💾][20241502tests] |
-| 20241601 | [Day 16: ?][20241601]                             | [💾][20241601solution]        | [💾][20241601tests]        |
-| 20241602 | [Day 16: ? - Part 2][20241602]                    | [💾][20241602solution]        | [💾][20241602tests]        |
+| 20241601 | [Day 16: Reindeer Maze][20241601]                 | ✅[💾][20241601solution] | ✅[💾][20241601tests] |
+| 20241602 | [Day 16: Reindeer Maze - Part 2][20241602]        | ✅[💾][20241602solution] | ✅[💾][20241602tests] |
 | 20241701 | [Day 17: ?][20241701]                             | [💾][20241701solution]        | [💾][20241701tests]        |
 | 20241702 | [Day 17: ? - Part 2][20241702]                    | [💾][20241702solution]        | [💾][20241702tests]        |
 | 20241801 | [Day 18: ?][20241801]                             | [💾][20241801solution]        | [💾][20241801tests]        |

adventofcode/src/main/java/org/ck/adventofcode/year2024/Day16.java

@@ -1,34 +1,187 @@
 package org.ck.adventofcode.year2024;
 
-import java.util.Scanner;
+import java.util.*;
+import java.util.function.ToLongBiFunction;
+import java.util.stream.Collectors;
 import org.ck.adventofcode.util.AOCSolution;
 import org.ck.codechallengelib.annotation.Solution;
 
 @Solution(
     id = 20241601,
-    name = "Day 16: ?",
+    name = "Day 16: Reindeer Maze",
     url = "https://adventofcode.com/2024/day/16",
-    category = "2024",
-    solved = false)
+    category = "2024")
 @Solution(
     id = 20241602,
-    name = "Day 16: ? - Part 2",
+    name = "Day 16: Reindeer Maze - Part 2",
     url = "https://adventofcode.com/2024/day/16#part2",
-    category = "2024",
-    solved = false)
+    category = "2024")
 public class Day16 extends AOCSolution {
 
   @Override
   protected void runPartOne(final Scanner in) {
-    run(in);
+    run(
+        in,
+        (cache, end) ->
+            getMinPoints(cache[end.y()][end.x()]).stream().findFirst().orElseThrow().points());
   }
 
   @Override
   protected void runPartTwo(final Scanner in) {
-    run(in);
+    run(in, this::getUniquePathElements);
   }
 
-  private void run(final Scanner in) {
-    print("Whoopsie");
+  private void run(
+      final Scanner in, final ToLongBiFunction<CacheValue[][][], Coordinate> getResult) {
+    final List<String> grid = new ArrayList<>();
+
+    Coordinate start = null;
+    Coordinate end = null;
+
+    int row = 0;
+    while (in.hasNextLine()) {
+      final String line = in.nextLine();
+
+      if (line.contains("S")) {
+        start = new Coordinate(line.indexOf('S'), row);
+      }
+      if (line.contains("E")) {
+        end = new Coordinate(line.indexOf('E'), row);
+      }
+
+      grid.add(line);
+      ++row;
+    }
+
+    if (start == null || end == null) {
+      throw new IllegalStateException();
+    }
+
+    final CacheValue[][][] cache = getCacheValues(grid, start);
+
+    print(getResult.applyAsLong(cache, end));
+  }
+
+  private static CacheValue[][][] getCacheValues(final List<String> grid, final Coordinate start) {
+    final Queue<State> queue = new PriorityQueue<>(Comparator.comparingLong(State::points));
+    queue.add(new State(new Position(start, Direction.EAST), null, 0));
+
+    final CacheValue[][][] cache = new CacheValue[grid.size()][grid.getFirst().length()][4];
+    for (int y = 0; y < cache.length; ++y) {
+      for (int x = 0; x < cache.length; ++x) {
+        for (int direction = 0; direction < 4; ++direction) {
+          cache[y][x][direction] = new CacheValue(Long.MAX_VALUE, new HashSet<>());
+        }
+      }
+    }
+
+    while (!queue.isEmpty()) {
+      final State state = queue.poll();
+      final Position current = state.current();
+      final Coordinate coordinate = current.coordinate();
+      final Direction direction = current.direction();
+      final long points = state.points();
+
+      if (cache[coordinate.y()][coordinate.x()][direction.ordinal()].points() < points) {
+        continue;
+      }
+      cache[coordinate.y()][coordinate.x()][direction.ordinal()] =
+          new CacheValue(points, cache[coordinate.y()][coordinate.x()][direction.ordinal()].from());
+      if (state.last() != null) {
+        cache[coordinate.y()][coordinate.x()][direction.ordinal()].from().add(state.last());
+      }
+
+      final Position next = direction.next(current);
+      if (grid.get(next.coordinate().y()).charAt(next.coordinate().x()) != '#') {
+        queue.add(new State(next, current, points + 1));
+      }
+
+      queue.add(new State(direction.turnCW(current), current, points + 1000));
+      queue.add(new State(direction.turnCCW(current), current, points + 1000));
+    }
+    return cache;
+  }
+
+  private Set<CacheValue> getMinPoints(final CacheValue[] cache) {
+    final long min =
+        Math.min(
+            Math.min(cache[0].points(), cache[1].points()),
+            Math.min(cache[2].points(), cache[3].points()));
+
+    return Arrays.stream(cache).filter(entry -> entry.points() == min).collect(Collectors.toSet());
+  }
+
+  private int getUniquePathElements(final CacheValue[][][] cache, final Coordinate end) {
+    final Queue<Position> queue =
+        getMinPoints(cache[end.y()][end.x()]).stream()
+            .map(CacheValue::from)
+            .flatMap(Set::stream)
+            .distinct()
+            .collect(Collectors.toCollection(LinkedList::new));
+    final Set<Coordinate> pathPieces = new HashSet<>();
+
+    while (!queue.isEmpty()) {
+      final Position position = queue.poll();
+
+      pathPieces.add(position.coordinate());
+
+      queue.addAll(
+          cache[position.coordinate().y()][position.coordinate().x()][
+              position.direction().ordinal()]
+              .from());
+    }
+
+    return pathPieces.size() + 1;
+  }
+
+  private record CacheValue(long points, Set<Position> from) {}
+
+  private record State(Position current, Position last, long points) {}
+
+  private record Position(Coordinate coordinate, Direction direction) {}
+
+  private record Coordinate(int x, int y) {}
+
+  private enum Direction {
+    NORTH(0, -1),
+    EAST(1, 0),
+    SOUTH(0, 1),
+    WEST(-1, 0);
+
+    private final int deltaX;
+    private final int deltaY;
+
+    Direction(int deltaX, int deltaY) {
+      this.deltaX = deltaX;
+      this.deltaY = deltaY;
+    }
+
+    public Position turnCW(final Position current) {
+      return new Position(
+          current.coordinate(),
+          switch (this) {
+            case NORTH -> Direction.EAST;
+            case EAST -> Direction.SOUTH;
+            case SOUTH -> Direction.WEST;
+            case WEST -> Direction.NORTH;
+          });
+    }
+
+    public Position turnCCW(final Position current) {
+      return new Position(
+          current.coordinate(),
+          switch (this) {
+            case NORTH -> Direction.WEST;
+            case EAST -> Direction.NORTH;
+            case SOUTH -> Direction.EAST;
+            case WEST -> Direction.SOUTH;
+          });
+    }
+
+    public Position next(Position current) {
+      return new Position(
+          new Coordinate(current.coordinate().x() + deltaX, current.coordinate().y() + deltaY),
+          current.direction());
+    }
   }
 }

adventofcode/src/test/java/org/ck/adventofcode/year2024/Day16Test.java

@@ -1,20 +1,18 @@
 package org.ck.adventofcode.year2024;
 
 import org.ck.adventofcode.util.BaseAOCTest;
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
-@Disabled
 class Day16Test extends BaseAOCTest {
   @ParameterizedTest
-  @ValueSource(strings = {"01a"})
+  @ValueSource(strings = {"01a", "01b"})
   void testPartOneExamples(final String name) throws Exception {
     runTest(new Day16()::partOne, "day16/%s".formatted(name));
   }
 
   @ParameterizedTest
-  @ValueSource(strings = {"02a"})
+  @ValueSource(strings = {"02a", "02b"})
   void testPartTwoExamples(final String name) throws Exception {
     runTest(new Day16()::partTwo, "day16/%s".formatted(name));
   }

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/01.result.txt

@@ -0,0 +1 @@
+127520

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/01a.result.txt

@@ -0,0 +1 @@
+7036

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/01a.txt

@@ -0,0 +1,15 @@
+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/01b.result.txt

@@ -0,0 +1 @@
+11048

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/01b.txt

@@ -0,0 +1,17 @@
+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/02.result.txt

@@ -0,0 +1 @@
+565

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/02a.result.txt

@@ -0,0 +1 @@
+45

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/02a.txt

@@ -0,0 +1,15 @@
+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/02b.result.txt

@@ -0,0 +1 @@
+64

adventofcode/src/test/resources/org/ck/adventofcode/year2024/day16/02b.txt

@@ -0,0 +1,17 @@
+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################