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DIRECTIONS = {
'L': (-1, 0),
'U': (0, -1),
'R': (1, 0),
'D': (0, 1),
}
def closest_apple_bot(board, position):
x, y = position
height = len(board)
width = len(board[0])
# todo contains the squares we need to explore
todo = []
# done contains the squares we've already explored
done = set()
# for each initial direction
for direction in DIRECTIONS:
dx, dy = DIRECTIONS[direction]
# find the new position
nx = (x + dx) % width
ny = (y + dy) % height
# add to todo and done
todo.append((nx, ny, direction))
done.add((nx, ny))
while todo:
# take the first item in todo
x, y, direction = todo.pop(0)
cell = board[y][x]
# if we've reached an apple, we've found the shortest path
# and direction is the right way to go
if cell == '*':
return direction
# if we can't move into this cell, go to the next square to explore
if cell != '.':
continue
# at this square, we can go any direction,
# as long as it's not in our done set
for dx, dy in DIRECTIONS.values():
nx = (x + dx) % width
ny = (y + dy) % height
if (nx, ny) not in done:
# we haven't visited this square before,
# add it to our list of squares to visit
# note that the third item here is the direction we initially
# took to get to this square
todo.append((nx, ny, direction))
done.add((nx, ny))
# if we get here, there are no apples on the board,
# so we'll just move up.
return 'U'
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