Day 12: Garden Groups

README.md

@@ -16,4 +16,4 @@ Development occurs in language-specific directories:
 |[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day9.kt)|[day9.py](py/aoc2024/day9.py)|[day9.rs](rs/src/day9.rs)|
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt)|[day10.py](py/aoc2024/day10.py)|[day10.rs](rs/src/day10.rs)|
 |[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt)|[day11.py](py/aoc2024/day11.py)|[day11.rs](rs/src/day11.rs)|
-|[Day12.hs](hs/src/Day12.hs)|[Day12.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day12.kt)|||
+|[Day12.hs](hs/src/Day12.hs)|[Day12.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day12.kt)|[day12.py](py/aoc2024/day12.py)||

py/aoc2024/day12.py

@@ -0,0 +1,146 @@
+"""
+Day 12: Garden Groups
+"""
+
+from collections import Counter, defaultdict
+import textwrap
+from typing import Generator
+
+SAMPLE_INPUT_1 = textwrap.dedent(
+    """\
+    AAAA
+    BBCD
+    BBCC
+    EEEC
+    """
+)
+SAMPLE_INPUT_2 = textwrap.dedent(
+    """\
+    OOOOO
+    OXOXO
+    OOOOO
+    OXOXO
+    OOOOO
+    """
+)
+SAMPLE_INPUT_3 = textwrap.dedent(
+    """\
+    RRRRIICCFF
+    RRRRIICCCF
+    VVRRRCCFFF
+    VVRCCCJFFF
+    VVVVCJJCFE
+    VVIVCCJJEE
+    VVIIICJJEE
+    MIIIIIJJEE
+    MIIISIJEEE
+    MMMISSJEEE
+    """
+)
+SAMPLE_INPUT_4 = textwrap.dedent(
+    """\
+    EEEEE
+    EXXXX
+    EEEEE
+    EXXXX
+    EEEEE
+    """
+)
+SAMPLE_INPUT_5 = textwrap.dedent(
+    """\
+    AAAAAA
+    AAABBA
+    AAABBA
+    ABBAAA
+    ABBAAA
+    AAAAAA
+    """
+)
+
+
+def _groups(data: str) -> Generator[set[tuple[int, int]]]:
+    lines = data.splitlines()
+    visited = set()
+    for y, line in enumerate(lines):
+        for x, char in enumerate(line):
+            group = set()
+            stack = [(y, x)]
+            while stack:
+                y2, x2 = pos = stack.pop()
+                if lines[y2][x2] != char or pos in visited:
+                    continue
+                visited.add(pos)
+                group.add(pos)
+                if 0 < y2:
+                    stack.append((y2 - 1, x2))
+                if 0 < x2:
+                    stack.append((y2, x2 - 1))
+                if x2 < len(lines[y2]) - 1:
+                    stack.append((y2, x2 + 1))
+                if y2 < len(lines) - 1:
+                    stack.append((y2 + 1, x2))
+            if group:
+                yield (group)
+
+
+def _perimeter1(group: set[tuple[int, int]]) -> int:
+    edges = Counter()
+    for y, x in group:
+        edges.update(
+            (
+                (2 * y - 1, 2 * x),
+                (2 * y, 2 * x - 1),
+                (2 * y, 2 * x + 1),
+                (2 * y + 1, 2 * x),
+            )
+        )
+    return sum(value == 1 for value in edges.values())
+
+
+def part1(data: str) -> int:
+    """
+    >>> part1(SAMPLE_INPUT_1)
+    140
+    >>> part1(SAMPLE_INPUT_2)
+    772
+    >>> part1(SAMPLE_INPUT_3)
+    1930
+    """
+    return sum(len(group) * _perimeter1(group) for group in _groups(data))
+
+
+def _perimeter2(group: set[tuple[int, int]]) -> int:
+    edges = defaultdict(set)
+    for y, x in group:
+        edges[(2 * y - 1, 2 * x)].add(0)
+        edges[(2 * y, 2 * x - 1)].add(1)
+        edges[(2 * y, 2 * x + 1)].add(3)
+        edges[(2 * y + 1, 2 * x)].add(2)
+    lines = defaultdict(set)
+    for (y, x), value in edges.items():
+        if len(value) == 1:
+            value = next(iter(value))
+            lines[x if value % 2 else y + 1].add((x + y, value))
+    return sum(
+        1 + sum(abs(q - p) > 2 or b != d for (q, b), (p, d) in zip(line, line[1:]))
+        for line in map(sorted, lines.values())
+    )
+
+
+def part2(data: str) -> int:
+    """
+    >>> part2(SAMPLE_INPUT_1)
+    80
+    >>> part2(SAMPLE_INPUT_2)
+    436
+    >>> part2(SAMPLE_INPUT_4)
+    236
+    >>> part2(SAMPLE_INPUT_5)
+    368
+    >>> part2(SAMPLE_INPUT_3)
+    1206
+    """
+    return sum(len(group) * _perimeter2(group) for group in _groups(data))
+
+
+parts = (part1, part2)

py/pyproject.toml

@@ -35,6 +35,7 @@ day8 = "aoc2024.day8:parts"
 day9 = "aoc2024.day9:parts"
 day10 = "aoc2024.day10:parts"
 day11 = "aoc2024.day11:parts"
+day12 = "aoc2024.day12:parts"
 
 [build-system]
 requires = ["poetry-core"]