day 16

aoc2023/day16.py

@@ -0,0 +1,176 @@
+import pathlib
+import sys
+from dataclasses import dataclass
+
+sys.setrecursionlimit(100000)
+
+
+base_dir = pathlib.Path(__file__).parent
+filename = base_dir / "day16_input.txt"
+
+with open(base_dir / filename) as f:
+    lines: list[str] = f.read().splitlines()
+
+
+@dataclass
+class Direction:
+    name: str
+    dx: int
+    dy: int
+
+    def __hash__(self) -> int:
+        return hash((self.dx, self.dy))
+
+
+@dataclass
+class Position:
+    x: int
+    y: int
+
+    def __add__(self, other: Direction) -> "Position":
+        return Position(self.x + other.dx, self.y + other.dy)
+
+    def __hash__(self):
+        return hash((self.x, self.y))
+
+
+class Grid:
+    def __init__(self, lines: list[list[str]]):
+        self.height = len(lines)
+        self.width = len(lines[0])
+        self.cells = lines
+
+    def validate_position(self, position: Position):
+        if position.x < 0 or position.y < 0:
+            raise IndexError(f"Out of bounds: {position.x=}, {position.y=}")
+        if position.x >= self.width or position.y >= self.height:
+            raise IndexError(f"Out of bounds: {position.x=}, {position.y=}")
+
+    def count(self, ch: str) -> int:
+        return sum(row.count(ch) for row in self.cells)
+
+    def show(self):
+        for row in self.cells:
+            print("".join(row))
+        print()
+
+    def __getitem__(self, position: Position) -> str:
+        self.validate_position(position)
+        return self.cells[position.y][position.x]
+
+    def __setitem__(self, position: Position, value: str):
+        self.validate_position(position)
+        self.cells[position.y][position.x] = value
+
+
+directions = {
+    "N": Direction("N", 0, -1),
+    "E": Direction("E", 1, 0),
+    "S": Direction("S", 0, 1),
+    "W": Direction("W", -1, 0),
+}
+piece_directions = {
+    ".": {
+        "N": ("N",),
+        "S": ("S",),
+        "E": ("E",),
+        "W": ("W",),
+    },
+    "-": {
+        "N": ("W", "E"),
+        "S": ("W", "E"),
+        "E": ("E",),
+        "W": ("W",),
+    },
+    "|": {
+        "N": ("N"),
+        "S": ("S"),
+        "E": ("N", "S"),
+        "W": ("N", "S"),
+    },
+    "/": {
+        "N": ("E",),
+        "S": ("W",),
+        "E": ("N",),
+        "W": ("S",),
+    },
+    "\\": {
+        "N": ("W",),
+        "S": ("E",),
+        "E": ("S",),
+        "W": ("N",),
+    },
+}
+
+
+def energize_grid(
+    grid: Grid,
+    energized: Grid,
+    position: Position,
+    direction: Direction,
+    seen: set[tuple[Position, Direction]] | None = None,
+):
+    if seen is None:
+        seen = set()
+
+    if (position, direction) in seen:
+        return
+
+    seen.add((position, direction))
+
+    try:
+        ch = grid[position]
+    except IndexError:
+        return
+
+    energized[position] = "#"
+
+    for direction_name in piece_directions[ch][direction.name]:
+        new_direction = directions[direction_name]
+        energize_grid(
+            grid,
+            energized,
+            position + new_direction,
+            new_direction,
+            seen=seen,
+        )
+
+
+def part_1():
+    grid = Grid([list(line) for line in lines])
+    energized = Grid([["." for _ in range(grid.width)] for _ in range(grid.height)])
+    energize_grid(grid, energized, Position(0, 0), directions["E"])
+    return energized.count("#")
+
+
+def part_2():
+    best = 0
+    grid = Grid([list(line) for line in lines])
+
+    for x in range(grid.width):
+        # top edge
+        energized = Grid([["." for _ in range(grid.width)] for _ in range(grid.height)])
+        energize_grid(grid, energized, Position(x, 0), directions["S"])
+        best = max(best, energized.count("#"))
+
+        # bottom edge
+        energized = Grid([["." for _ in range(grid.width)] for _ in range(grid.height)])
+        energize_grid(grid, energized, Position(x, grid.height - 1), directions["N"])
+        best = max(best, energized.count("#"))
+
+    for y in range(grid.height):
+        # left edge
+        energized = Grid([["." for _ in range(grid.width)] for _ in range(grid.height)])
+        energize_grid(grid, energized, Position(0, y), directions["E"])
+        best = max(best, energized.count("#"))
+
+        # right edge
+        energized = Grid([["." for _ in range(grid.width)] for _ in range(grid.height)])
+        energize_grid(grid, energized, Position(grid.width - 1, y), directions["W"])
+        best = max(best, energized.count("#"))
+
+    return best
+
+
+print(f"answer_p1 = {part_1()}")
+print(f"answer_p2 = {part_2()}")

aoc2023/day16_test.txt

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+.|...\....
+|.-.\.....
+.....|-...
+........|.
+..........
+.........\
+..../.\\..
+.-.-/..|..
+.|....-|.\
+..//.|....