Day 6: Guard Gallivant

README.md

@@ -10,4 +10,4 @@ Development occurs in language-specific directories:
 |[Day3.hs](hs/src/Day3.hs)|[Day3.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day3.kt)|[day3.py](py/aoc2024/day3.py)|[day3.rs](rs/src/day3.rs)|
 |[Day4.hs](hs/src/Day4.hs)|[Day4.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day4.kt)|[day4.py](py/aoc2024/day4.py)|[day4.rs](rs/src/day4.rs)|
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
-|[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|||
+|[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)||

py/aoc2024/day6.py

@@ -0,0 +1,108 @@
+"""
+Day 6: Guard Gallivant
+"""
+
+from functools import partial
+from multiprocessing import Pool
+from typing import Generator, Iterable, Set, Tuple
+
+SAMPLE_INPUT = """
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...
+"""
+
+
+def _parse(data: str) -> Tuple[Tuple[int, int], Tuple[int, int], Set[Tuple[int, int]]]:
+    obstructions = []
+    for y, line in enumerate(filter(None, data.splitlines())):
+        for x, char in enumerate(line):
+            match char:
+                case "^":
+                    initial_y, initial_x = y, x
+                case "#":
+                    obstructions.append((y, x))
+    return (initial_y, initial_x), (y + 1, len(line)), frozenset(obstructions)
+
+
+def _visit(
+    initial_pos: Tuple[int, int],
+    max_bounds: Tuple[int, int],
+    obstructions: Iterable[Tuple[int, int]],
+) -> Generator[Tuple[int, int], None, Set[Tuple[int, int]]]:
+    y, x = initial_pos
+    dy, dx = -1, 0
+    max_y, max_x = max_bounds
+    visited = set()
+    while True:
+        yield (y, x), (dy, dx)
+        visited.add((y, x))
+        next_y, next_x = y + dy, x + dx
+        if next_y not in range(max_y) or next_x not in range(max_x):
+            break
+        if (next_y, next_x) in obstructions:
+            dy, dx = dx, -dy
+        else:
+            y, x = next_y, next_x
+    return visited
+
+
+def _part1(
+    initial_pos: Tuple[int, int],
+    max_bounds: Tuple[int, int],
+    obstructions: Iterable[Tuple[int, int]],
+) -> Set[Tuple[int, int]]:
+    visitor = _visit(initial_pos, max_bounds, obstructions)
+    while True:
+        try:
+            next(visitor)
+        except StopIteration as error:
+            return error.value
+
+
+def part1(data: str) -> int:
+    """
+    >>> part1(SAMPLE_INPUT)
+    41
+    """
+    initial_pos, max_bounds, obstructions = _parse(data)
+    return len(_part1(initial_pos, max_bounds, obstructions))
+
+
+def _part2(
+    initial_pos: Tuple[int, int],
+    max_bounds: Tuple[int, int],
+    obstructions: Iterable[Tuple[int, int]],
+) -> bool:
+    visited = set()
+    for key in _visit(initial_pos, max_bounds, obstructions):
+        if key in visited:
+            return True
+        visited.add(key)
+    return False
+
+
+def part2(data: str, concurrency: int = None) -> int:
+    """
+    >>> part2(SAMPLE_INPUT)
+    6
+    """
+    initial_pos, max_bounds, obstructions = _parse(data)
+    candidates = _part1(initial_pos, max_bounds, obstructions) - {initial_pos}
+    with Pool(concurrency) as pool:
+        return sum(
+            pool.imap_unordered(
+                partial(_part2, initial_pos, max_bounds),
+                (obstructions | {candidate} for candidate in candidates),
+            )
+        )
+
+
+parts = (part1, part2)

py/pyproject.toml

@@ -12,7 +12,7 @@ python = "^3.13"
 natsort = "^8.4.0"
 
 [tool.poetry.group.dev.dependencies]
-ruff = "^0.8.1"
+ruff = "^0.8.2"
 pytest = "^8.3.4"
 pytest-benchmark = { version = "^5.1.0", extras = ["histogram"] }
 
@@ -29,6 +29,7 @@ day2 = "aoc2024.day2:parts"
 day3 = "aoc2024.day3:parts"
 day4 = "aoc2024.day4:parts"
 day5 = "aoc2024.day5:parts"
+day6 = "aoc2024.day6:parts"
 
 [build-system]
 requires = ["poetry-core"]