124 lines
2.9 KiB
Python
124 lines
2.9 KiB
Python
from typing import NamedTuple
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test_input = """
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....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...
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""".strip()
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test_solution_p1 = 41
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test_solution_p2 = 6
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def solve_p1(puzzle_input: str) -> int:
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map_info = _parse_map(puzzle_input)
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traversal_analysis = _traverse_map(map_info)
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unique_locations = set((a, b) for a, b, _ in traversal_analysis.visited)
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return len(unique_locations)
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def solve_p2(puzzle_input: str) -> int:
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map_info = _parse_map(puzzle_input)
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added_obstacles_candidates = set()
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for i, line in enumerate(map_info.map):
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for j, cell in enumerate(line):
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if not cell:
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map_info.map[i][j] = True
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if _traverse_map(map_info).stuck:
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added_obstacles_candidates.add((i, j))
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map_info.map[i][j] = False
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# Remove guard location from candidates
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added_obstacles_candidates.discard((map_info.guard[:2]))
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return len(added_obstacles_candidates)
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class MapInfo(NamedTuple):
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map: list[list[bool]]
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guard: tuple[int, int, str]
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def _parse_map(puzzle_input: str) -> MapInfo:
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puzzle_map = []
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guard = None
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for x, line in enumerate(puzzle_input.split("\n")):
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if not line:
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continue
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line_list = list()
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for y, cell in enumerate(line):
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if cell in "^v<>":
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guard = (x, y, cell)
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line_list.append(cell == "#")
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puzzle_map.append(line_list)
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assert guard is not None, "Guard not found in map"
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assert all(
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len(line) == len(puzzle_map[0]) for line in puzzle_map
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), "Map is not rectangular"
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return MapInfo(puzzle_map, guard)
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class TraversalAnalysis(NamedTuple):
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visited: set[tuple[int, int]]
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stuck: bool
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_rotation_map = {
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"^": ">",
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"v": "<",
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"<": "^",
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">": "v",
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}
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def _traverse_map(map_info: MapInfo) -> TraversalAnalysis:
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x, y, direction = map_info.guard
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visited = set()
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visited.add((x, y, direction))
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while True:
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# Determine next cell
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match direction:
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case "^":
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next_x, next_y = x - 1, y
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case "v":
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next_x, next_y = x + 1, y
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case "<":
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next_x, next_y = x, y - 1
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case ">":
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next_x, next_y = x, y + 1
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# Guard patrols out of bounds
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if (
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next_x < 0
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or next_x >= len(map_info.map)
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or next_y < 0
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or next_y >= len(map_info.map[0])
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):
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break
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# Turn right if an obstacle is encountered
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if map_info.map[next_x][next_y]:
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direction = _rotation_map[direction]
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# Otherwise, move to next cell
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else:
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x, y = next_x, next_y
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if (x, y, direction) in visited:
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return TraversalAnalysis(visited, True)
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visited.add((x, y, direction))
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return TraversalAnalysis(visited, False)
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