day21 python part a

AOC/data/day_21/dataset.txt

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+805A
+964A
+459A
+968A
+671A

AOC/data/day_21/sample_part_one.txt

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+029A
+980A
+179A
+456A
+379A

AOC/data/day_21/sample_part_two.txt

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+029A
+980A
+179A
+456A
+379A

AOC/python/solutions/day_21.py

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+from functools import cache
+
+from helpers.grid_helpers import find_char
+from models.aoc_solution import AOCSolution
+
+type Coord = tuple[int, int]
+
+
+class Day21(AOCSolution):
+    EXPECTED = {
+        "part_one": {"sample": 126384, "data": 278748},
+        "part_two": {"sample": 0, "data": 0},
+    }
+
+    def __post_init__(self) -> None:
+        self.codes = self.data.splitlines()
+        self.keypad = [
+            ["7", "8", "9"],
+            ["4", "5", "6"],
+            ["1", "2", "3"],
+            [None, "0", "A"],
+        ]
+        self.directions = [
+            [None, "^", "A"],
+            ["<", "v", ">"],
+        ]
+        self.key_start = find_char(self.keypad, "A")
+        self.dir_start = find_char(self.directions, "A")
+        self.numpad_paths.cache_clear()
+
+    @cache
+    def numpad_paths(self, start: str, end: str, is_numpad: bool) -> set[str]:
+        """Generate all paths between start and end avoiding None tiles"""
+        grid = self.keypad if is_numpad else self.directions
+        x, y = find_char(grid, start)
+        x2, y2 = find_char(grid, end)
+        dx, dy = x2 - x, y2 - y
+        paths: set[str] = set()
+        path = f"{'<>'[dx > 0] * abs(dx)}{'^v'[dy > 0] * abs(dy)}"
+        if grid[y][x + dx] is not None:
+            paths.add(f"{path}A")
+        if grid[y + dy][x] is not None:
+            paths.add(f"{path[::-1]}A")
+        return paths
+
+    def code_paths(self, code: str, is_numpad: bool) -> set[str]:
+        """Generate all paths for a given code"""
+        if len(code) < 2:
+            return {""}
+        starts = self.numpad_paths(code[0], code[1], is_numpad)
+        return {
+            start + path
+            for start in starts
+            for path in self.code_paths(code[1:], is_numpad)
+        }
+
+    def generate_parent_paths(self, code: str) -> set[str]:
+        """Generate all paths for a given code"""
+        paths = self.code_paths(f"A{code}", True)
+        parent_paths = set()
+        for _ in range(2):
+            parent_paths = set()
+            for path in paths:
+                parent_paths.update(self.code_paths(f"A{path}", False))
+            paths = parent_paths
+        return parent_paths
+
+    def part_one(self) -> int:
+        total = 0
+        for code in self.codes:
+            paths = self.generate_parent_paths(code)
+            shortest = min(len(path) for path in paths)
+            numeric = int(code[:-1])
+            total += numeric * shortest
+        return total
+
+    def part_two(self) -> int:
+        return 0
+
+
+if __name__ == "__main__":
+    Day21().run()