2024 day 12 parts 1

README.md

@@ -15,7 +15,7 @@
 - 2021 - ★★★★★ ★★★★★ ★★★★★ ★★★
 - 2022 - ★★★★★ ★★★★★ ★★★★★ ★☆
 - 2023 - ★★★★★ ★★★★★ ★★★★★ ★★★☆
-- 2024 - ★★★★★ ★★★★★ ★
+- 2024 - ★★★★★ ★★★★★ ★☆
 
 ## How to use
 

src/year2024/day12a.py

@@ -0,0 +1,77 @@
+"""2024 - Day 12 Part 1: Garden Groups"""
+
+from __future__ import annotations
+
+SHIFTS = (
+    # r c
+    (-1, 0),  # up
+    (0, +1),  # right
+    (+1, 0),  # down
+    (0, -1),  # left
+)
+
+
+class Region:
+    def __init__(self, key: str, area: int = 1, perimeter: int = 0) -> None:
+        self.key = key
+        self.area = area
+        self.perimeter = perimeter
+
+    @classmethod
+    def from_point(
+        cls, sr: int, sc: int, data: list[str], seen: set[tuple[int, int]]
+    ) -> Region:
+        rows = len(data)
+        cols = len(data[0])
+
+        region = Region(key=data[sr][sc])
+        to_process = [(sr, sc)]
+
+        while to_process:
+            r, c = to_process.pop()
+
+            for dr, dc in SHIFTS:
+                nr = r + dr
+                nc = c + dc
+
+                if not (0 <= nr < rows and 0 <= nc < cols):
+                    region.perimeter += 1
+                    # todo: flaky false positive below
+                elif data[nr][nc] != region.key:
+                    region.perimeter += 1
+                elif (nr, nc) not in seen:
+                    region.area += 1
+                    to_process.append((nr, nc))
+                    seen.add((nr, nc))
+
+        return region
+
+    @property
+    def price(self) -> int:
+        return self.area * self.perimeter
+
+    def __str__(self) -> str:
+        return f"Region(key='{self.key}')"
+
+
+def parse_regions(data: list[str]) -> list[Region]:
+    rows = len(data)
+    cols = len(data[0])
+
+    seen: set[tuple[int, int]] = set()
+    regions: list[Region] = []
+
+    for r in range(rows):
+        for c in range(cols):
+            if (r, c) not in seen:
+                seen.add((r, c))
+                region = Region.from_point(r, c, data, seen)
+                regions.append(region)
+
+    return regions
+
+
+def solve(task: str) -> int:
+    data = task.split("\n")
+    regions = parse_regions(data)
+    return sum(x.price for x in regions)

tests/src/year2024/test_day12a.py

@@ -0,0 +1,48 @@
+"""2024 - Day 12 Part 1: Garden Groups"""
+
+from textwrap import dedent
+
+from src.year2024.day12a import solve
+
+
+def test_solve_1():
+    task = dedent(
+        """
+        AAAA
+        BBCD
+        BBCC
+        EEEC
+        """
+    ).strip()
+    assert solve(task) == 140
+
+
+def test_solve_2():
+    task = dedent(
+        """
+        OOOOO
+        OXOXO
+        OOOOO
+        OXOXO
+        OOOOO
+        """
+    ).strip()
+    assert solve(task) == 772
+
+
+def test_solve_3():
+    task = dedent(
+        """
+        RRRRIICCFF
+        RRRRIICCCF
+        VVRRRCCFFF
+        VVRCCCJFFF
+        VVVVCJJCFE
+        VVIVCCJJEE
+        VVIIICJJEE
+        MIIIIIJJEE
+        MIIISIJEEE
+        MMMISSJEEE
+        """
+    ).strip()
+    assert solve(task) == 1930