advent-of-code/2023/day16.py

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import os
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import sys
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from typing import Literal, TypeAlias, cast
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VERBOSE = os.getenv("AOC_VERBOSE") == "True"
CellType: TypeAlias = Literal[".", "|", "-", "\\", "/"]
Direction: TypeAlias = Literal["R", "L", "U", "D"]
Mappings: dict[
CellType,
dict[
Direction,
tuple[tuple[tuple[int, int, Direction], ...], tuple[Direction, ...]],
],
] = {
".": {
"R": (((0, +1, "R"),), ("R", "L")),
"L": (((0, -1, "L"),), ("R", "L")),
"U": (((-1, 0, "U"),), ("U", "D")),
"D": (((+1, 0, "D"),), ("U", "D")),
},
"-": {
"R": (((0, +1, "R"),), ("R", "L")),
"L": (((0, -1, "L"),), ("R", "L")),
"U": (((0, +1, "R"), (0, -1, "L")), ("U", "D")),
"D": (((0, +1, "R"), (0, -1, "L")), ("U", "D")),
},
"|": {
"U": (((-1, 0, "U"),), ("U", "D")),
"D": (((+1, 0, "D"),), ("U", "D")),
"R": (((-1, 0, "U"), (+1, 0, "D")), ("R", "L")),
"L": (((-1, 0, "U"), (+1, 0, "D")), ("R", "L")),
},
"/": {
"R": (((-1, 0, "U"),), ("R", "D")),
"L": (((+1, 0, "D"),), ("L", "U")),
"U": (((0, +1, "R"),), ("U", "L")),
"D": (((0, -1, "L"),), ("R", "D")),
},
"\\": {
"R": (((+1, 0, "D"),), ("R", "U")),
"L": (((-1, 0, "U"),), ("L", "D")),
"U": (((0, -1, "L"),), ("U", "R")),
"D": (((0, +1, "R"),), ("L", "D")),
},
}
def propagate(
layout: list[list[CellType]], start: tuple[int, int], direction: Direction
) -> list[list[tuple[Direction, ...]]]:
n_rows, n_cols = len(layout), len(layout[0])
beams: list[list[tuple[Direction, ...]]] = [
[() for _ in range(len(layout[0]))] for _ in range(len(layout))
]
queue = [(start, direction)]
while queue:
(row, col), direction = queue.pop()
if (
row not in range(0, n_rows)
or col not in range(0, n_cols)
or direction in beams[row][col]
):
continue
moves, update = Mappings[layout[row][col]][direction]
beams[row][col] += update
for move in moves:
queue.append(((row + move[0], col + move[1]), move[2]))
return beams
layout: list[list[CellType]] = [
[cast(CellType, col) for col in row] for row in sys.stdin.read().splitlines()
]
beams = propagate(layout, (0, 0), "R")
if VERBOSE:
print("\n".join(["".join("#" if col else "." for col in row) for row in beams]))
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# part 1
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answer_1 = sum(sum(map(bool, row)) for row in beams)
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print(f"answer 1 is {answer_1}")
# part 2
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n_rows, n_cols = len(layout), len(layout[0])
cases: list[tuple[tuple[int, int], Direction]] = []
for row in range(n_rows):
cases.append(((row, 0), "R"))
cases.append(((row, n_cols - 1), "L"))
for col in range(n_cols):
cases.append(((0, col), "D"))
cases.append(((n_rows - 1, col), "U"))
answer_2 = max(
sum(sum(map(bool, row)) for row in propagate(layout, start, direction))
for start, direction in cases
)
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print(f"answer 2 is {answer_2}")