sudoku solver problem

[masterofpuppets]

hii everybody,

I have a weird problem with a program for solving sudoku puzzles. I am representing the puzzle as a list of lists of lists containing all the possibillities for a single square and my problem is that when I try to remove a single appearance of a number from a square, the number is removed from all the squares in the grid. I am using the .remove() function and I am not sure why it is behaving like that. Here is the code I am having trouble with...

def eliminate( grid, square, value ):
row = square[ 0 ]; col = square[ 1 ]
poss = grid[ row ][ col ]
if len( poss ) > 1:
poss.remove( value )
grid[ row ][ col ] = poss
# if len( poss ) == 1:
# fixValue( grid, square, poss[ 0 ] )

'square' is a tuple representing the ( row, column ) of the square
'grid' is the whole grid
'value' is the value to be removed from the possibillities for the current square
At the end when I try to print the grid all the squares are changed with the result for 'poss'
If you need other pieces of the code I'll post them here...

[Ancient Dragon]

>>If you need other pieces of the code I'll post them here...

Please don't. Post all your technical questions in one of the language boards. I would move this to the right place if I knew what computer language that code was written in.

[masterofpuppets]

:) sorry about that I'm still new to the website. The code is written in Python :)

[shadwickman]

Also, please put your code in [code]

[/code] tags next time so that the indentation is kept, as it's a crucial part of Python.

Other than that, I'm still confused what you are having a problem with. Maybe the removing of the number from the whole square has to do with a different bit of your code - say if you're calling this eliminate function in a loop somewhere else which is causing the error.
Please just try to rephrase your question to be a little bit clearer, thanks.

[lllllIllIlllI]

def eliminate( grid, square, value ):
    row = square[ 0 ]
    col = square[ 1 ]
    poss = grid[ row ][ col ]
    if len( poss ) > 1:
        poss.remove( value )
    grid[ row ][ col ] = poss
    # if len( poss ) == 1:
    # fixValue( grid, square, poss[ 0 ] )

I think i got the indentation right :P

And can you do a printout of what the list 'grid' looks like? That might be able to help, just one grid though. Not every one.

[woooee]

when I try to remove a single appearance of a number from a square, the number is removed from all the squares in the grid

Generally that means that you are not declaring a list of independent lists but a list of references to the same list. Show us how you are creating "grid", and/or loop through and print id(this_sub_list) and see if the addresses are the same.

##---  This declares a 3X5 list and prints the memory address
grid = []
for j in range(0, 3):
   grid.append([ [] for x in range(5) ])
print grid

for j in range(0, 3):
   for k in range(0, 5):
      print id(grid[j][k])

Edit: Based on shadwickman's post, you probably did something like

##--- declare a 1X3 list for testing
grid = []
sub = []
for j in range(0, 3):
   grid.append(sub)
print grid

for j in range(0, 3):
   print id(grid[j])     ## they are all the same

[shadwickman]

Ah, good point, I hadn't thought of that. This illustrates what woooee means:

>>> a = b = []
>>> a.append('hi')
>>> a.append('world!')
>>> a
['hi', 'world!']
>>> b.remove('hi')
>>> b
['world!']
>>> a
['world!']
>>> id(a) == id(b)  # same address in memory
True

They both refer to the same list because of the way they were declared ( a = b = [] ), so both names are actually for only one list.

[masterofpuppets]

Thanks for the replies guys. As you mentioned the problem was that all the elements in the 'grid' list had the same id, because instead of adding the numbers 1-9 to a list and then in the 'grid' list, I added a list that contained the numbers 1-9, e.g. tmp = [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
Thanks a lot for your help :)