From c8cde6a4c86c6e0e2502da6f5ba16f83f6e14a5a Mon Sep 17 00:00:00 2001
From: Nettika <git@nettika.cat>
Date: Tue, 10 Dec 2024 18:50:20 -0800
Subject: [PATCH] Implement day 10 solver

---
 puzzles/10.py | 138 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 puzzles/10.py

diff --git a/puzzles/10.py b/puzzles/10.py
new file mode 100644
index 0000000..63a58f4
--- /dev/null
+++ b/puzzles/10.py
@@ -0,0 +1,138 @@
+from dataclasses import dataclass
+from textwrap import dedent
+from typing import NamedTuple, override
+from unittest import TestCase
+
+from puzzles._solver import Solver
+
+
+class TrailSet(NamedTuple):
+    trailhead: tuple[int, int]
+    trailends: set[tuple[int, int]]
+    count: int
+
+
+@dataclass
+class TopographicalMap:
+    grid: list[list[str]]
+    trailheads: set[tuple[int, int]]
+
+    @classmethod
+    def parse(cls, raw_map: str) -> "TopographicalMap":
+        grid = []
+        trailheads = set()
+
+        for x, row in enumerate(raw_map.strip().splitlines()):
+            grid_row = []
+
+            for y, cell in enumerate(row):
+                height = int(cell)
+                grid_row.append(height)
+                if height == 0:
+                    trailheads.add((x, y))
+
+            grid.append(grid_row)
+
+        return cls(grid, trailheads)
+
+    def trails(self) -> list[TrailSet]:
+        trails = []
+
+        for trailhead in self.trailheads:
+            trailends: set[tuple, tuple] = set()
+            count = 0
+            x, y = trailhead
+            height = self.grid[x][y]
+
+            def follow_trail(x, y, height):
+                nonlocal count
+
+                if height == 9:
+                    trailends.add((x, y))
+                    count += 1
+                    return
+
+                if x > 0 and self.grid[x - 1][y] == height + 1:
+                    follow_trail(x - 1, y, height + 1)
+                if x < len(self.grid) - 1 and self.grid[x + 1][y] == height + 1:
+                    follow_trail(x + 1, y, height + 1)
+                if y > 0 and self.grid[x][y - 1] == height + 1:
+                    follow_trail(x, y - 1, height + 1)
+                if y < len(self.grid[0]) - 1 and self.grid[x][y + 1] == height + 1:
+                    follow_trail(x, y + 1, height + 1)
+
+            follow_trail(x, y, height)
+
+            trails.append(TrailSet(trailhead, trailends, count))
+
+        return trails
+
+
+class DayTenSolver(Solver):
+    topographical_map: TopographicalMap
+
+    @override
+    def __init__(self, puzzle_input: str):
+        self.topographical_map = TopographicalMap.parse(puzzle_input)
+
+    @override
+    def solve_p1(self) -> int:
+        trail_sets = self.topographical_map.trails()
+        return sum(len(trail_set.trailends) for trail_set in trail_sets)
+
+    @override
+    def solve_p2(self) -> int:
+        trail_sets = self.topographical_map.trails()
+        return sum(trail_set.count for trail_set in trail_sets)
+
+
+class TestDayTenSolver(TestCase):
+    test_input = dedent(
+        """
+        89010123
+        78121874
+        87430965
+        96549874
+        45678903
+        32019012
+        01329801
+        10456732
+        """
+    )
+
+    def test_parse(self):
+        solver = DayTenSolver(self.test_input)
+        self.assertEqual(
+            solver.topographical_map,
+            TopographicalMap(
+                grid=[
+                    [8, 9, 0, 1, 0, 1, 2, 3],
+                    [7, 8, 1, 2, 1, 8, 7, 4],
+                    [8, 7, 4, 3, 0, 9, 6, 5],
+                    [9, 6, 5, 4, 9, 8, 7, 4],
+                    [4, 5, 6, 7, 8, 9, 0, 3],
+                    [3, 2, 0, 1, 9, 0, 1, 2],
+                    [0, 1, 3, 2, 9, 8, 0, 1],
+                    [1, 0, 4, 5, 6, 7, 3, 2],
+                ],
+                trailheads={
+                    (0, 2),
+                    (0, 4),
+                    (2, 4),
+                    (4, 6),
+                    (5, 2),
+                    (5, 5),
+                    (6, 0),
+                    (6, 6),
+                    (7, 1),
+                },
+            ),
+        )
+
+    def test_solve_p1(self):
+        solver = DayTenSolver(self.test_input)
+        self.assertEqual(solver.solve_p1(), 36)
+
+    def test_solve_p2(self):
+        solver = DayTenSolver(self.test_input)
+        self.assertEqual(solver.solve_p2(), 81)