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# nested lists as arrays

Hi, I'm using nested lists as arrays and having some problems with
that approach. In my puzzle class there is a swapelement method which
doesn't work out. Any help and comments on the code will be
appreciated. Thanks.

# Puzzle.py
# class for a sliding block puzzle

# an starting state of a 8-puzzle could look like the following:
# where X is an empty space and the move up in the example would move
6 to X
# X is represented as -1 in the array
# ------------
# | 7 2 4 |
# | |
# | 5 X 6 |
# | |
# | 8 3 1 |
# ------------

# the goal is to reach this state:
# ------------
# | X 1 2 |
# | |
# | 3 4 5 |
# | |
# | 6 7 8 |
# ------------

import copy

class Puzzle:

def __init__(self, dim):
self.dim = dim
self.elements = [[0 for column in range(dim)] for row in
range(dim) ]

def getEmptySlot(self):
i = 0
j = 0
while i <= self.dim-1:
while j <= self.dim-1:
if self.elements[j][i] == -1:
return [j, i]
j = j+1
j = 0
i = i + 1

def performMove(self, direction):
slot = self.getEmptySlot()

if (direction == "up"):
self.swapElements(slot[1], slot[0], slot[1]+1, slot[0])
elif (direction == "down"):
self.swapElements(slot[1], slot[0], slot[1]-1, slot[0])
elif direction == "left":
self.swapElements(slot[1], slot[0], slot[1], slot[0]-1)
elif (direction == "right"):
self.swapElements(slot[1], slot[0], slot[1], slot[0]+1)

def swapElements(self, fromx, fromy, tox, toy):
dummy = self.elements[toy][tox]

self.elements[toy][tox] = self.elements[fromy][fromx]
self.elements[fromy][fromx] = dummy

def getPossibleMoves(self):
emptySlot = self.getEmptySlot()
y = emptySlot[1]
x = emptySlot[0]
north = (y == 0)
south = (y == (self.dim-1))
west = (x == 0)
east = (x == (self.dim-1))

middle = not(north or south or west or east)

northwest = north and west
northeast = north and east
southwest = south and west
southeast = south and east
# orientation has to be distinct
# save original values
orignorth = north
origsouth = south
# original north or south
orignors = north or south

north = north and not (west or east)
south = south and not (west or east)
west = west and not (orignors)
east = east and not (orignors)

if middle:
return ["up", "down", "left", "right"]
elif north:
return ["up", "left", "right"]
elif south:
return ["down", "left", "right"]
elif west:
return ["up", "down", "left"]
elif east:
return ["up", "down", "right"]
elif northwest:
return ["up", "left"]
elif northeast:
return ["up", "right"]
elif southwest:
return ["down", "left"]
elif southeast:
return ["down", "right"]

# ~Puzzle.py
Jul 18 '05 #1
5 1530
"naturalborncyborg" <be*************@blawrc.de> wrote:
Hi, I'm using nested lists as arrays and having some problems with
that approach. In my puzzle class there is a swapelement method which
doesn't work out.
what happens, and what do you expect?
Any help and comments on the code will be appreciated.

is it elements[y][x] or elements[x][y]? both variants seem to be used
in your code.

(fwiw, in this case, using a dictionary might be a lot easier. store cells
as elements[x, y], use elements.get((x, y)) is None to check for empty
cells, use elements[x, y] = None or del elements[x, y] to empty a cell,
use elements = {} to clear all cells, etc).

</F>

Jul 18 '05 #2
naturalborncyborg wrote:
Hi, I'm using nested lists as arrays and having some problems with
that approach. In my puzzle class there is a swapelement method which
doesn't work out.

What "doesn't work out"? On casual inspection that method seems to "work":
p = Puzzle(2)
p.elements[0][0] = 1
p.elements[1][1] = 2
p.elements [[1, 0], [0, 2]] p.swapElements(0,0,1,1)
p.elements [[2, 0], [0, 1]]

What should it do instead?

Michael

Jul 18 '05 #3
Allright. What difference in runtime and space would it make using
dictionaries instead?

Do you have a pointer for me concerning runtime of standard
manipulations in Pythons?

Thanks for tip.

Jul 18 '05 #4
Allright. What difference in runtime and space would it make using
dictionaries instead?

Do you have a pointer for me concerning runtime of standard
manipulations in Pythons?

Thanks for the tip.

Jul 18 '05 #5
be*************@blawrc.de wrote:
Allright. What difference in runtime and space would it make using
dictionaries instead?

is this for an interactive game? if so, the answer is "none at all".

(on my machine, you can make about 6000000 dict[x,y] accesses per
second, compared to 7500000 list[x][y] accesses... assuming that your
algorithm needs to check each cell on the board 10 times per move, and
you want the moves to appear "instantly", the slower solution should be
fast enough for a 250x250 board, compared to a 270x270 board for the
faster solution...).

</F>

Jul 18 '05 #6

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