Weighing in at 18203 characters is a Python solution that can:
- cope with mirrors outside of the
'room'
- calculate the trajectory when there is no 'room' on the basis of 2D limitations (the spec says lots about what has to be in the 'room' but not if the room has to exist)
- report back on errors
It still needs tidied up somewhat and I do not know if 2D physics dictate that the beam cannot cross itself...
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
The shortest code by character count to input a 2D representation of a board,
and output 'true' or 'false' according to the input.
The board is made out of 4 types of tiles:
# - A solid wall
x - The target the laser has to hit
/ or \ - Mirrors pointing to a direction (depends on laser direction)
v, ^, > or < - The laser pointing to a direction (down, up, right and left
respectively)
There is only one laser and only one target. Walls must form a solid rectangle
of any size, where the laser and target are placed inside. Walls inside the
'room' are possible.
Laser ray shots and travels from it's origin to the direction it's pointing. If
a laser ray hits the wall, it stops. If a laser ray hits a mirror, it is bounces
90 degrees to the direction the mirror points to. Mirrors are two sided, meaning
both sides are 'reflective' and may bounce a ray in two ways. If a laser ray
hits the laser (^v><) itself, it is treated as a wall (laser beam destroys the
beamer and so it'll never hit the target).
"""
SOLID_WALL, TARGET, MIRROR_NE_SW, MIRROR_NW_SE, LASER_DOWN, LASER_UP, \
LASER_RIGHT, LASER_LEFT = range(8)
MIRRORS = (MIRROR_NE_SW, MIRROR_NW_SE)
LASERS = (LASER_DOWN, LASER_UP, LASER_RIGHT, LASER_LEFT)
DOWN, UP, RIGHT, LEFT = range(4)
LASER_DIRECTIONS = {
LASER_DOWN : DOWN,
LASER_UP : UP,
LASER_RIGHT: RIGHT,
LASER_LEFT : LEFT
}
ROW, COLUMN = range(2)
RELATIVE_POSITIONS = {
DOWN : (ROW, 1),
UP : (ROW, -1),
RIGHT: (COLUMN, 1),
LEFT : (COLUMN, -1)
}
TILES = {"#" : SOLID_WALL,
"x" : TARGET,
"/" : MIRROR_NE_SW,
"\\": MIRROR_NW_SE,
"v" : LASER_DOWN,
"^" : LASER_UP,
">" : LASER_RIGHT,
"<" : LASER_LEFT}
REFLECTIONS = {MIRROR_NE_SW: {DOWN : LEFT,
UP : RIGHT,
RIGHT: UP,
LEFT : DOWN},
MIRROR_NW_SE: {DOWN : RIGHT,
UP : LEFT,
RIGHT: DOWN,
LEFT : UP}}
def does_laser_hit_target(tiles):
"""
Follows a lasers trajectory around a grid of tiles determining if it
will reach the target.
Keyword arguments:
tiles --- row/column based version of a board containing symbolic
versions of the tiles (walls, laser, target, etc)
"""
#Obtain the position of the laser
laser_pos = get_laser_pos(tiles)
#Retrieve the laser's tile
laser = get_tile(tiles, laser_pos)
#Create an editable starting point for the beam
beam_pos = list(laser_pos)
#Create an editable direction for the beam
beam_dir = LASER_DIRECTIONS[laser]
#Cache the number of rows
number_of_rows = len(tiles)
#Keep on looping until an ultimate conclusion
while True:
#Discover the axis and offset the beam is travelling to
axis, offset = RELATIVE_POSITIONS[beam_dir]
#Modify the beam's position
beam_pos[axis] += offset
#Allow for a wrap around in this 2D scenario
try:
#Get the beam's new tile
tile = get_tile(tiles, beam_pos)
#Perform wrapping
except IndexError:
#Obtain the row position
row_pos = beam_pos[ROW]
#Handle vertical wrapping
if axis == ROW:
#Handle going off the top
if row_pos == -1:
#Move beam to the bottom
beam_pos[ROW] = number_of_rows - 1
#Handle going off the bottom
elif row_pos == number_of_rows:
#Move beam to the top
beam_pos[ROW] = 0
#Handle horizontal wrapping
elif axis == COLUMN:
#Obtain the row
row = tiles[row_pos]
#Calculate the number of columns
number_of_cols = len(row)
#Obtain the column position
col_pos = beam_pos[COLUMN]
#Handle going off the left hand side
if col_pos == -1:
#Move beam to the right hand side
beam_pos[COLUMN] = number_of_cols - 1
#Handle going off the right hand side
elif col_pos == number_of_cols:
#Move beam to the left hand side
beam_pos[COLUMN] = 0
#Get the beam's new tile
tile = get_tile(tiles, beam_pos)
#Handle hitting a wall or the laser
if tile in LASERS \
or tile == SOLID_WALL:
return False
#Handle hitting the target
if tile == TARGET:
return True
#Handle hitting a mirror
if tile in MIRRORS:
beam_dir = reflect(tile, beam_dir)
def get_laser_pos(tiles):
"""
Returns the current laser position or an exception.
Keyword arguments:
tiles --- row/column based version of a board containing symbolic
versions of the tiles (walls, laser, target, etc)
"""
#Calculate the number of rows
number_of_rows = len(tiles)
#Loop through each row by index
for row_pos in range(number_of_rows):
#Obtain the current row
row = tiles[row_pos]
#Calculate the number of columns
number_of_cols = len(row)
#Loop through each column by index
for col_pos in range(number_of_cols):
#Obtain the current column
tile = row[col_pos]
#Handle finding a laser
if tile in LASERS:
#Return the laser's position
return row_pos, col_pos
def get_tile(tiles, pos):
"""
Retrieves a tile at the position specified.
Keyword arguments:
pos --- a row/column position of the tile
tiles --- row/column based version of a board containing symbolic
versions of the tiles (walls, laser, target, etc)
"""
#Obtain the row position
row_pos = pos[ROW]
#Obtain the column position
col_pos = pos[COLUMN]
#Obtain the row
row = tiles[row_pos]
#Obtain the tile
tile = row[col_pos]
#Return the tile
return tile
def get_wall_pos(tiles, reverse=False):
"""
Keyword arguments:
tiles --- row/column based version of a board containing symbolic
versions of the tiles (walls, laser, target, etc)
reverse --- whether to search in reverse order or not (defaults to no)
"""
number_of_rows = len(tiles)
row_iter = range(number_of_rows)
if reverse:
row_iter = reversed(row_iter)
for row_pos in row_iter:
row = tiles[row_pos]
number_of_cols = len(row)
col_iter = range(number_of_cols)
if reverse:
col_iter = reversed(col_iter)
for col_pos in col_iter:
tile = row[col_pos]
if tile == SOLID_WALL:
pos = row_pos, col_pos
if reverse:
offset = -1
else:
offset = 1
for axis in ROW, COLUMN:
next_pos = list(pos)
next_pos[axis] += offset
try:
next_tile = get_tile(tiles, next_pos)
except IndexError:
next_tile = None
if next_tile != SOLID_WALL:
raise WallOutsideRoomError(row_pos, col_pos)
return pos
def identify_tile(tile):
"""
Returns a symbolic value for every identified tile or None.
Keyword arguments:
tile --- the tile to identify
"""
#Safely lookup the tile
try:
#Return known tiles
return TILES[tile]
#Handle unknown tiles
except KeyError:
#Return a default value
return
def main():
"""
Takes a board from STDIN and either returns a result to STDOUT or an
error to STDERR.
Called when this file is run on the command line.
"""
#As this function is the only one to use this module, and it can only be
#called once in this configuration, it makes sense to only import it here.
import sys
#Reads the board from standard input.
board = sys.stdin.read()
#Safely handles outside input
try:
#Calculates the result of shooting the laser
result = shoot_laser(board)
#Handles multiple item errors
except (MultipleLaserError, MultipleTargetError) as error:
#Display the error
sys.stderr.write("%s\n" % str(error))
#Loop through all the duplicated item symbols
for symbol in error.symbols:
#Highlight each symbol in green
board = board.replace(symbol, "\033[01;31m%s\033[m" % symbol)
#Display the board
sys.stderr.write("%s\n" % board)
#Exit with an error signal
sys.exit(1)
#Handles item missing errors
except (NoLaserError, NoTargetError) as error:
#Display the error
sys.stderr.write("%s\n" % str(error))
#Display the board
sys.stderr.write("%s\n" % board)
#Exit with an error signal
sys.exit(1)
#Handles errors caused by symbols
except (OutsideRoomError, WallNotRectangleError) as error:
#Displays the error
sys.stderr.write("%s\n" % str(error))
lines = board.split("\n")
line = lines[error.row_pos]
before = line[:error.col_pos]
after = line[error.col_pos + 1:]
symbol = line[error.col_pos]
line = "%s\033[01;31m%s\033[m%s" % (before, symbol, after)
lines[error.row_pos] = line
board = "\n".join(lines)
#Display the board
sys.stderr.write("%s\n" % board)
#Exit with an error signal
sys.exit(1)
#Handles errors caused by non-solid walls
except WallNotSolidError as error:
#Displays the error
sys.stderr.write("%s\n" % str(error))
lines = board.split("\n")
line = lines[error.row_pos]
before = line[:error.col_pos]
after = line[error.col_pos + 1:]
symbol = line[error.col_pos]
line = "%s\033[01;5;31m#\033[m%s" % (before, after)
lines[error.row_pos] = line
board = "\n".join(lines)
#Display the board
sys.stderr.write("%s\n" % board)
#Exit with an error signal
sys.exit(1)
#If a result was returned
else:
#Converts the result into a string
result_str = str(result)
#Makes the string lowercase
lower_result = result_str.lower()
#Returns the result
sys.stdout.write("%s\n" % lower_result)
def parse_board(board):
"""
Interprets the raw board syntax and returns a grid of tiles.
Keyword arguments:
board --- the board containing the tiles (walls, laser, target, etc)
"""
#Create a container for all the lines
tiles = list()
#Loop through all the lines of the board
for line in board.split("\n"):
#Identify all the tiles on the line
row = [identify_tile(tile) for tile in line]
#Add the row to the container
tiles.append(row)
#Return the container
return tiles
def reflect(mirror, direction):
"""
Returns an updated laser direction after it has been reflected on a
mirror.
Keyword arguments:
mirror --- the mirror to reflect the laser from
direction --- the direction the laser is travelling in
"""
try:
direction_lookup = REFLECTIONS[mirror]
except KeyError:
raise TypeError("%s is not a mirror.", mirror)
try:
return direction_lookup[direction]
except KeyError:
raise TypeError("%s is not a direction.", direction)
def shoot_laser(board):
"""
Shoots the boards laser and returns whether it will hit the target.
Keyword arguments:
board --- the board containing the tiles (walls, laser, target, etc)
"""
tiles = parse_board(board)
validate_board(tiles)
return does_laser_hit_target(tiles)
def validate_board(tiles):
"""
Checks an board to see if it is valid and raises an exception if not.
Keyword arguments:
tiles --- row/column based version of a board containing symbolic
versions of the tiles (walls, laser, target, etc)
"""
found_laser = False
found_target = False
try:
n_wall, w_wall = get_wall_pos(tiles)
s_wall, e_wall = get_wall_pos(tiles, reverse=True)
except TypeError:
n_wall = e_wall = s_wall = w_wall = None
number_of_rows = len(tiles)
for row_pos in range(number_of_rows):
row = tiles[row_pos]
number_of_cols = len(row)
for col_pos in range(number_of_cols):
tile = row[col_pos]
if ((row_pos in (n_wall, s_wall) and
col_pos in range(w_wall, e_wall))
or
(col_pos in (e_wall, w_wall) and
row_pos in range(n_wall, s_wall))):
if tile != SOLID_WALL:
raise WallNotSolidError(row_pos, col_pos)
elif (n_wall != None and
(row_pos < n_wall or
col_pos > e_wall or
row_pos > s_wall or
col_pos < w_wall)):
if tile in LASERS:
raise LaserOutsideRoomError(row_pos, col_pos)
elif tile == TARGET:
raise TargetOutsideRoomError(row_pos, col_pos)
elif tile == SOLID_WALL:
if not (row_pos >= n_wall and
col_pos <= e_wall and
row_pos <= s_wall and
col_pos >= w_wall):
raise WallOutsideRoomError(row_pos, col_pos)
else:
if tile in LASERS:
if not found_laser:
found_laser = True
else:
raise MultipleLaserError(row_pos, col_pos)
elif tile == TARGET:
if not found_target:
found_target = True
else:
raise MultipleTargetError(row_pos, col_pos)
if not found_laser:
raise NoLaserError(tiles)
if not found_target:
raise NoTargetError(tiles)
class LasersError(Exception):
"""Parent Error Class for all errors raised."""
pass
class NoLaserError(LasersError):
"""Indicates that there are no lasers on the board."""
symbols = "^v><"
def __str__ (self):
return "No laser (%s) to fire." % ", ".join(self.symbols)
class NoTargetError(LasersError):
"""Indicates that there are no targets on the board."""
symbols = "x"
def __str__ (self):
return "No target (%s) to hit." % ", ".join(self.symbols)
class MultipleLaserError(LasersError):
"""Indicates that there is more than one laser on the board."""
symbols = "^v><"
def __str__ (self):
return "Too many lasers (%s) to fire, only one is allowed." % \
", ".join(self.symbols)
class MultipleTargetError(LasersError):
"""Indicates that there is more than one target on the board."""
symbols = "x"
def __str__ (self):
return "Too many targets (%s) to hit, only one is allowed." % \
", ".join(self.symbols)
class WallNotSolidError(LasersError):
"""Indicates that the perimeter wall is not solid."""
__slots__ = ("__row_pos", "__col_pos", "n_wall", "s_wall", "e_wall",
"w_wall")
def __init__(self, row_pos, col_pos):
self.__row_pos = row_pos
self.__col_pos = col_pos
def __str__ (self):
return "Walls must form a solid rectangle."
def __get_row_pos(self):
return self.__row_pos
def __get_col_pos(self):
return self.__col_pos
row_pos = property(__get_row_pos)
col_pos = property(__get_col_pos)
class WallNotRectangleError(LasersError):
"""Indicates that the perimeter wall is not a rectangle."""
__slots__ = ("__row_pos", "__col_pos")
def __init__(self, row_pos, col_pos):
self.__row_pos = row_pos
self.__col_pos = col_pos
def __str__ (self):
return "Walls must form a rectangle."
def __get_row_pos(self):
return self.__row_pos
def __get_col_pos(self):
return self.__col_pos
row_pos = property(__get_row_pos)
col_pos = property(__get_col_pos)
class OutsideRoomError(LasersError):
"""Indicates an item is outside of the perimeter wall."""
__slots__ = ("__row_pos", "__col_pos", "__name")
def __init__(self, row_pos, col_pos, name):
self.__row_pos = row_pos
self.__col_pos = col_pos
self.__name = name
def __str__ (self):
return "A %s was found outside of a 'room'." % self.__name
def __get_row_pos(self):
return self.__row_pos
def __get_col_pos(self):
return self.__col_pos
row_pos = property(__get_row_pos)
col_pos = property(__get_col_pos)
class LaserOutsideRoomError(OutsideRoomError):
"""Indicates the laser is outside of the perimeter wall."""
def __init__ (self, row_pos, col_pos):
OutsideRoomError.__init__(self, row_pos, col_pos, "laser")
class TargetOutsideRoomError(OutsideRoomError):
"""Indicates the target is outside of the perimeter wall."""
def __init__ (self, row_pos, col_pos):
OutsideRoomError.__init__(self, row_pos, col_pos, "target")
class WallOutsideRoomError(OutsideRoomError):
"""Indicates that there is a wall outside of the perimeter wall."""
def __init__ (self, row_pos, col_pos):
OutsideRoomError.__init__(self, row_pos, col_pos, "wall")
if __name__ == "__main__":
main()
A bash script to show off the colour error reporting:
#!/bin/bash
declare -a TESTS
test() {
echo -e "\033[1m$1\033[0m"
tput sgr0
echo "$2" | ./lasers.py
echo
}
test \
"no laser" \
" ##########
# x #
# / #
# /#
# \\ #
##########"
test \
"multiple lasers" \
" ##########
# v x #
# / #
# /#
# \\ ^ #
##########"
test \
"no target" \
" ##########
# v #
# / #
# /#
# \\ #
##########"
test \
"multiple targets" \
" ##########
# v x #
# / #
# /#
# \\ x #
##########"
test \
"wall not solid" \
" ##### ####
# v x #
# / #
# /#
# \\ #
##########"
test \
"laser_outside_room" \
" ##########
> # x #
# / #
# /#
# \\ #
##########"
test \
"laser before room" \
" > ##########
# x #
# / #
# /#
# \\ #
##########"
test \
"laser row before room" \
" >
##########
# x #
# / #
# /#
# \\ #
##########"
test \
"laser after room" \
" ##########
# x #
# / #
# /#
# \\ #
########## >"
test \
"laser row after room" \
" ##########
# x #
# / #
# /#
# \\ #
##########
> "
test \
"target outside room" \
" ##########
x # v #
# / #
# /#
# \\ #
##########"
test \
"target before room" \
" x ##########
# v #
# / #
# /#
# \\ #
##########"
test \
"target row before room" \
" x
##########
# v #
# / #
# /#
# \\ #
##########"
test \
"target after room" \
" ##########
# v #
# / #
# /#
# \\ #
########## x"
test \
"target row after room" \
" ##########
# v #
# / #
# /#
# \\ #
##########
x "
test \
"wall outside room" \
" ##########
# # v #
# / #
# /#
# \\ x #
##########"
test \
"wall before room" \
" # ##########
# v #
# / #
# /#
# \\ x #
##########"
test \
"wall row before room" \
" #
##########
# v #
# / #
# /#
# \\ x #
##########"
test \
"wall after room" \
" ##########
# v #
# / #
# /#
# \\ x #
########## #"
test \
"wall row after room" \
" ##########
# v #
# / #
# /#
# \\ x #
##########
#"
test \
"mirror outside room positive" \
" ##########
/ # / \\ #
# #
# \\ x#
# > / #
########## "
test \
"mirrors outside room negative" \
" ##########
\\ # v x #
# / #
# /#
# \\ #
##########"
test \
"mirror before room positive" \
" \\ ##########
# / \\ #
# #
# \\ x#
# > / #
########## "
test \
"mirrors before room negative" \
" / ##########
# v x #
# / #
# /#
# \\ #
##########"
test \
"mirror row before room positive" \
" \\
##########
# / \\ #
# #
# \\ x#
# > / #
########## "
test \
"mirrors row before room negative" \
" \\
##########
# v x #
# / #
# /#
# \\ #
##########"
test \
"mirror after row positive" \
" ##########
# / \\ #
# #
# \\ x#
# > / #
########## / "
test \
"mirrors after row negative" \
" ##########
# v x #
# / #
# /#
# \\ #
########## / "
test \
"mirror row after row positive" \
" ##########
# / \\ #
# #
# \\ x#
# > / #
##########
/ "
test \
"mirrors row after row negative" \
" ##########
# v x #
# / #
# /#
# \\ #
##########
/ "
test \
"laser hitting laser" \
" ##########
# v \\#
# #
# #
#x \\ /#
##########"
test \
"mirrors positive" \
" ##########
# / \\ #
# #
# \\ x#
# > / #
########## "
test \
"mirrors negative" \
" ##########
# v x #
# / #
# /#
# \\ #
##########"
test \
"wall collision" \
" #############
# # #
# > # #
# # #
# # x #
# # #
#############"
test \
"extreme example" \
" ##########
#/\\/\\/\\ #
#\\\\//\\\\\\ #
#//\\/\\/\\\\#
#\\/\\/\\/x^#
##########"
test \
"brian example 1" \
"##########
# / \\ #
# #
#/ \\ x#
#\\> / #
##########"
test \
"brian example 2" \
"##########
# / \\#
# / \\ #
#/ \\ x#
#\\^/\\ / #
##########"
The unittests used in development:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import unittest
from lasers import *
class TestTileRecognition(unittest.TestCase):
def test_solid_wall(self):
self.assertEqual(SOLID_WALL, identify_tile("#"))
def test_target(self):
self.assertEqual(TARGET, identify_tile("x"))
def test_mirror_ne_sw(self):
self.assertEqual(MIRROR_NE_SW, identify_tile("/"))
def test_mirror_nw_se(self):
self.assertEqual(MIRROR_NW_SE, identify_tile("\\"))
def test_laser_down(self):
self.assertEqual(LASER_DOWN, identify_tile("v"))
def test_laser_up(self):
self.assertEqual(LASER_UP, identify_tile("^"))
def test_laser_right(self):
self.assertEqual(LASER_RIGHT, identify_tile(">"))
def test_laser_left(self):
self.assertEqual(LASER_LEFT, identify_tile("<"))
def test_other(self):
self.assertEqual(None, identify_tile(" "))
class TestReflection(unittest.TestCase):
def setUp(self):
self.DIRECTION = LEFT
self.NOT_DIRECTIO