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from collections import deque
def parse_input(file):
with open(file, 'r') as f:
maze = [list(line.strip()) for line in f]
return maze
def find_start_end(maze):
start = end = None
for r, row in enumerate(maze):
for c, val in enumerate(row):
if val == 'S':
start = (r, c)
elif val == 'E':
end = (r, c)
return start, end
def get_neighbors(pos, direction, maze):
directions = [(0, 1), (1, 0), (0, -1), (-1, 0)] # East, South, West, North
r, c = pos
neighbors = []
# Move forward
dr, dc = directions[direction]
if maze[r + dr][c + dc] != '#':
neighbors.append(((r + dr, c + dc), direction, 1)) # 1 point for moving forward
# Turn clockwise
neighbors.append((pos, (direction + 1) % 4, 1000)) # 1000 points for turning
# Turn counterclockwise
neighbors.append((pos, (direction - 1) % 4, 1000)) # 1000 points for turning
return neighbors
def find_best_paths(maze, start, end):
directions = [(0, 1), (1, 0), (0, -1), (-1, 0)] # East, South, West, North
start_direction = 0 # Start facing East
queue = deque([(start, start_direction, 0)]) # (position, direction, score)
visited = set()
best_score = float('inf')
best_paths = set()
while queue:
pos, direction, score = queue.popleft()
if (pos, direction) in visited:
continue
visited.add((pos, direction))
if pos == end:
if score < best_score:
best_score = score
best_paths = {pos}
elif score == best_score:
best_paths.add(pos)
continue
for neighbor, new_direction, cost in get_neighbors(pos, direction, maze):
new_score = score + cost
if new_score <= best_score:
queue.append((neighbor, new_direction, new_score))
if new_score == best_score:
best_paths.add(neighbor)
return best_paths
def count_best_path_tiles(maze, best_paths):
count = 0
for r, row in enumerate(maze):
for c, val in enumerate(row):
if (r, c) in best_paths and val != '#':
count += 1
return count
def main():
file = "input.txt"
maze = parse_input(file)
start, end = find_start_end(maze)
best_paths = find_best_paths(maze, start, end)
result = count_best_path_tiles(maze, best_paths)
print(result)
main() |