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Subject: Re: Sudoku
From: Eric Parry <joan4eric@gmail.com>
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Xref: csiph.com comp.lang.python:42352

On Saturday, March 30, 2013 8:41:08 AM UTC+10:30, Dave Angel wrote:
> On 03/29/2013 05:47 PM, Eric Parry wrote:
> 
> >
> 
> >>   <SNIP>
> 
> >>
> 
> > That explains why the program keeps running after a solution is found.
> 
> 
> 
> A recursive function can be designed to find all solutions, in which 
> 
> case it would (as you say) keep running.
> 
> 
> 
> The function you posted in the first place uses exit() to avoid keeping 
> 
> running.  It stops as soon as a solution is found.
> 
> 
> 
> Sometimes a problem cannot be solved in the number of stack entries 
> 
> supplied by Python.  So even though such a function will terminate, it 
> 
> may crash first if the problem is too big.  Example, the factorial 
> 
> problem I described earlier, if you pass it 2000 as a parameter.  If 
> 
> this is a problem, one can tell the Python to give you more stack entries.
> 
> 
> 
> Given a 9x9 matrix, and at least some of them filled in, the maximum 
> 
> depth your code can use is less than 81.  So it won't get a stack 
> 
> overflow in any implementation of Python I've seen.  Perhaps in an 8051.
> 
> 
> 
> Sometimes a bug in such a function will cause it to run indefinitely, 
> 
> and/or to overflow the stack.  I don't see such a bug in this function.
> 
> 
> 
> 
> 
> -- 
> 
> DaveA

The exit() did not work.
I replaced it with return = 0, and that does work.
Eric.