AoC 2025 Day 7 - java

Author: pareronia

README.md

@@ -9,7 +9,7 @@
 | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
 | ---| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
 | python3 | [✓](src/main/python/AoC2025_01.py) | [✓](src/main/python/AoC2025_02.py) | [✓](src/main/python/AoC2025_03.py) | [✓](src/main/python/AoC2025_04.py) | [✓](src/main/python/AoC2025_05.py) | [✓](src/main/python/AoC2025_06.py) | [✓](src/main/python/AoC2025_07.py) |  |  |  |  |  |
-| java | [✓](src/main/java/AoC2025_01.java) | [✓](src/main/java/AoC2025_02.java) | [✓](src/main/java/AoC2025_03.java) | [✓](src/main/java/AoC2025_04.java) | [✓](src/main/java/AoC2025_05.java) | [✓](src/main/java/AoC2025_06.java) |  |  |  |  |  |  |
+| java | [✓](src/main/java/AoC2025_01.java) | [✓](src/main/java/AoC2025_02.java) | [✓](src/main/java/AoC2025_03.java) | [✓](src/main/java/AoC2025_04.java) | [✓](src/main/java/AoC2025_05.java) | [✓](src/main/java/AoC2025_06.java) | [✓](src/main/java/AoC2025_07.java) |  |  |  |  |  |
 | bash | [✓](src/main/bash/AoC2025_01.sh) | [✓](src/main/bash/AoC2025_02.sh) | [✓](src/main/bash/AoC2025_03.sh) | [✓](src/main/bash/AoC2025_04.sh) | [✓](src/main/bash/AoC2025_05.sh) | [✓](src/main/bash/AoC2025_06.sh) |  |  |  |  |  |  |
 <!-- @END:ImplementationsTable:2025@ -->
 

src/main/java/AoC2025_07.java

@@ -0,0 +1,126 @@
+import static java.util.stream.Collectors.toSet;
+
+import com.github.pareronia.aoc.CharGrid;
+import com.github.pareronia.aoc.Grid.Cell;
+import com.github.pareronia.aoc.geometry.Direction;
+import com.github.pareronia.aoc.solution.Sample;
+import com.github.pareronia.aoc.solution.Samples;
+import com.github.pareronia.aoc.solution.SolutionBase;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.stream.Stream;
+
+@SuppressWarnings({"PMD.ClassNamingConventions", "PMD.NoPackage"})
+public final class AoC2025_07 extends SolutionBase<CharGrid, Long, Long> {
+
+    public static final char SPLITTER = '^';
+    public static final char START = 'S';
+
+    private AoC2025_07(final boolean debug) {
+        super(debug);
+    }
+
+    public static AoC2025_07 create() {
+        return new AoC2025_07(false);
+    }
+
+    public static AoC2025_07 createDebug() {
+        return new AoC2025_07(true);
+    }
+
+    @Override
+    protected CharGrid parseInput(final List<String> inputs) {
+        return CharGrid.from(inputs);
+    }
+
+    @Override
+    public Long solvePart1(final CharGrid grid) {
+        final Set<Integer> beams = grid.getAllEqualTo(START).map(Cell::getCol).collect(toSet());
+        long ans = 0L;
+        final Iterable<Cell> splitters = () -> grid.getAllEqualTo(SPLITTER).iterator();
+        for (final Cell splitter : splitters) {
+            if (beams.contains(splitter.getCol())) {
+                ans++;
+                beams.remove(splitter.getCol());
+                for (final Direction direction : Set.of(Direction.LEFT, Direction.RIGHT)) {
+                    beams.add(splitter.at(direction).getCol());
+                }
+            }
+        }
+        return ans;
+    }
+
+    @Override
+    public Long solvePart2(final CharGrid grid) {
+        class DFS {
+            private final Cell start;
+            private final Set<Cell> splitters;
+            private final Map<Cell, Long> cache = new HashMap<>();
+
+            DFS() {
+                this.start = grid.getAllEqualTo(START).findFirst().orElseThrow();
+                this.splitters = grid.getAllEqualTo(SPLITTER).collect(toSet());
+                splitters.add(this.start);
+            }
+
+            long dfs(final Cell cell) {
+                final long ans;
+                if (this.cache.containsKey(cell)) {
+                    ans = this.cache.get(cell);
+                } else {
+                    if (cell.equals(this.start)) {
+                        ans = 1;
+                    } else {
+                        ans =
+                                grid.getCellsN(cell)
+                                        .takeWhile(n -> !this.splitters.contains(n))
+                                        .flatMap(
+                                                n ->
+                                                        Stream.of(Direction.LEFT, Direction.RIGHT)
+                                                                .map(n::at))
+                                        .filter(this.splitters::contains)
+                                        .mapToLong(this::dfs)
+                                        .sum();
+                    }
+                    this.cache.put(cell, ans);
+                }
+                return ans;
+            }
+        }
+
+        final Cell bottomLeft = Cell.at(grid.getMaxRowIndex(), 0);
+        final DFS dfs = new DFS();
+        return dfs.dfs(bottomLeft) + grid.getCellsE(bottomLeft).mapToLong(dfs::dfs).sum();
+    }
+
+    @Samples({
+        @Sample(method = "part1", input = TEST, expected = "21"),
+        @Sample(method = "part2", input = TEST, expected = "40"),
+    })
+    public static void main(final String[] args) throws Exception {
+        create().run();
+    }
+
+    private static final String TEST =
+            """
+            .......S.......
+            ...............
+            .......^.......
+            ...............
+            ......^.^......
+            ...............
+            .....^.^.^.....
+            ...............
+            ....^.^...^....
+            ...............
+            ...^.^...^.^...
+            ...............
+            ..^...^.....^..
+            ...............
+            .^.^.^.^.^...^.
+            ...............
+            """;
+}