From 7e5e6b10a29d4eae1b926fdb452e5ab537eed9ea Mon Sep 17 00:00:00 2001
From: Nettika <git@nettika.cat>
Date: Wed, 11 Dec 2024 22:42:59 -0800
Subject: [PATCH] Implement day 12 solver

---
 puzzles/12.py  | 196 +++++++++++++++++++++++++++++++++++++++++++++++++
 pyproject.toml |   2 +-
 2 files changed, 197 insertions(+), 1 deletion(-)
 create mode 100644 puzzles/12.py

diff --git a/puzzles/12.py b/puzzles/12.py
new file mode 100644
index 0000000..4418ca5
--- /dev/null
+++ b/puzzles/12.py
@@ -0,0 +1,196 @@
+from dataclasses import dataclass
+from functools import cached_property
+from itertools import count
+from textwrap import dedent
+from typing import Iterator, NamedTuple, override
+from unittest import TestCase
+
+from more_itertools import first_true, ilen
+from multidict import MultiDict
+
+from puzzles._solver import Solver
+
+
+@dataclass(frozen=True)
+class Fence:
+    inside: tuple[int, int]
+    outside: tuple[int, int]
+
+    def left(self) -> "Fence":
+        (xi, yi) = self.inside
+        (xo, yo) = self.outside
+        dx, dy = (xo - xi, yo - yi)
+        return Fence((xi + dy, yi + dx), (xo + dy, yo + dx))
+
+    def right(self) -> "Fence":
+        (xi, yi) = self.inside
+        (xo, yo) = self.outside
+        dx, dy = (xo - xi, yo - yi)
+        return Fence((xi - dy, yi - dx), (xo - dy, yo - dx))
+
+
+@dataclass
+class Region:
+    label: str
+    plants: set[tuple[int, int]]
+
+    @property
+    def area(self) -> int:
+        return len(self.plants)
+
+    @cached_property
+    def fences(self) -> set[Fence]:
+        return {
+            Fence((x, y), (x + dx, y + dy))
+            for x, y in self.plants
+            for dx, dy in ((0, 1), (1, 0), (0, -1), (-1, 0))
+            if (x + dx, y + dy) not in self.plants
+        }
+
+    @property
+    def perimeter(self) -> int:
+        return len(self.fences)
+
+    @cached_property
+    def sides(self) -> set[tuple[int, int]]:
+        fence_ids: dict[Fence, int] = {}
+        id_gen = count(0)
+
+        for fence in self.fences:
+            if fence in fence_ids:
+                continue
+
+            id = next(id_gen)
+            fence_ids[fence] = id
+
+            left_fence = fence.left()
+            while left_fence in self.fences:
+                fence_ids[left_fence] = id
+                left_fence = left_fence.left()
+
+            right_fence = fence.right()
+            while right_fence in self.fences:
+                fence_ids[right_fence] = id
+                right_fence = right_fence.right()
+
+        return len(set(fence_ids.values()))
+
+
+class DayTwelveSolver(Solver):
+    regions: MultiDict[Region]
+
+    @override
+    def __init__(self, puzzle_input: str):
+        self.regions = MultiDict()
+
+        for x, row in enumerate(puzzle_input.strip().splitlines()):
+            for y, plant in enumerate(row):
+                if plant not in self.regions:
+                    self.regions.add(plant, Region(plant, {(x, y)}))
+                    continue
+
+                similar_regions = self.regions.popall(plant)
+                merge_top_region = first_true(
+                    similar_regions,
+                    None,
+                    pred=lambda region: (x - 1, y) in region.plants,
+                )
+                merge_left_region = first_true(
+                    similar_regions,
+                    None,
+                    pred=lambda region: (x, y - 1) in region.plants,
+                )
+
+                if merge_top_region:
+                    similar_regions.remove(merge_top_region)
+                    merge_top_region.plants.add((x, y))
+                    if merge_left_region and merge_left_region is not merge_top_region:
+                        similar_regions.remove(merge_left_region)
+                        merge_top_region.plants.update(merge_left_region.plants)
+                    self.regions.add(plant, merge_top_region)
+
+                elif merge_left_region:
+                    similar_regions.remove(merge_left_region)
+                    merge_left_region.plants.add((x, y))
+                    self.regions.add(plant, merge_left_region)
+
+                else:
+                    self.regions.add(plant, Region(plant, {(x, y)}))
+
+                self.regions.extend(
+                    [(plant, similar_region) for similar_region in similar_regions]
+                )
+
+    @override
+    def solve_p1(self) -> int:
+        return sum(region.area * region.perimeter for region in self.regions.values())
+
+    @override
+    def solve_p2(self) -> int:
+        return sum(region.area * region.sides for region in self.regions.values())
+
+
+class TestDayTwelveSolver(TestCase):
+    def test_solve_p1(self):
+        solver = DayTwelveSolver(
+            dedent(
+                """
+                AAAA
+                BBCD
+                BBCC
+                EEEC
+                """
+            )
+        )
+        self.assertEqual(solver.solve_p1(), 140)
+
+        solver = DayTwelveSolver(
+            dedent(
+                """
+                RRRRIICCFF
+                RRRRIICCCF
+                VVRRRCCFFF
+                VVRCCCJFFF
+                VVVVCJJCFE
+                VVIVCCJJEE
+                VVIIICJJEE
+                MIIIIIJJEE
+                MIIISIJEEE
+                MMMISSJEEE
+                """
+            )
+        )
+        self.assertEqual(solver.solve_p1(), 1930)
+
+    def test_solve_p2(self):
+        solver = DayTwelveSolver(
+            dedent(
+                """
+                AAAA
+                BBCD
+                BBCC
+                EEEC
+                """
+            )
+        )
+        for region in solver.regions.values():
+            print(region.label, region.sides)
+        self.assertEqual(solver.solve_p2(), 80)
+
+        solver = DayTwelveSolver(
+            dedent(
+                """
+                RRRRIICCFF
+                RRRRIICCCF
+                VVRRRCCFFF
+                VVRCCCJFFF
+                VVVVCJJCFE
+                VVIVCCJJEE
+                VVIIICJJEE
+                MIIIIIJJEE
+                MIIISIJEEE
+                MMMISSJEEE
+                """
+            )
+        )
+        self.assertEqual(solver.solve_p2(), 1206)
diff --git a/pyproject.toml b/pyproject.toml
index 91a43bd..31adc03 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -2,4 +2,4 @@
 name = "advent-of-code-2024"
 version = "0.0.0"
 description = "Advent of Code 2024"
-dependencies = ["advent", "more-itertools"]
+dependencies = ["advent", "more-itertools", "multidict"]