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Re: Sudoku

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On Friday, March 29, 2013 9:15:36 AM UTC+10:30, Chris Angelico wrote:
> On Fri, Mar 29, 2013 at 9:11 AM, Eric Parry <joan4eric@gmail.com> wrote:
> 
> > Thank you for that explanation.
> 
> > No, I do not understand recursion. It is missing from my Python manual. I would be pleased to receive further explanation from anyone.
> 
> 
> 
> If you already know what recursion is, just remember the answer.
> 
> Otherwise, find someone who is standing closer to Douglas Hofstadter
> 
> than you are; then ask him or her what recursion is.
> 
> 
> 
> :)
> 
> 
> 
> Recursion is a form of self-referential code. Take this simple, and
> 
> rather silly, means of calculating the sum of numbers in a list (like
> 
> the sum() function):
> 
> 
> 
> # The sum of numbers in an empty list is 0.
> 
> # Otherwise it is the first number plus the sum of the rest of the list.
> 
> def list_sum(lst):
> 
>     if not lst: return 0
> 
>     return lst[0] + list_sum(lst[1:])
> 
> 
> 
> >>> list_sum([1,2,3,4,5,6])
> 
> 21
> 
> 
> 
> Note how the function calls itself - but not always. That's critical
> 
> to recursion - a termination condition. In this case, it's quite
> 
> obvious that the list will eventually have nothing left in it, so the
> 
> function will terminate. Sometimes it's less obvious. Sometimes a bug
> 
> results in infinite recursion... and:
> 
> 
> 
> RuntimeError: maximum recursion depth exceeded in comparison
> 
> 
> 
> Hope that helps!
> 
> 
> 
> ChrisA

Thank you for that example Chris.
That explains why the program keeps running after a solution is found.
Eric

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Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-26 22:44 -0700
  Re: Sudoku Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2013-03-27 08:58 +0100
    Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-27 20:00 -0700
      Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-28 00:36 -0400
        Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-28 15:11 -0700
          Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-28 19:28 -0400
            Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-28 22:07 -0700
            Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-28 22:07 -0700
          Re: Sudoku Chris Angelico <rosuav@gmail.com> - 2013-03-29 09:45 +1100
            Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-29 14:47 -0700
              Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-29 18:11 -0400
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-30 15:06 -0700
                Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-30 19:15 -0400
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-31 15:03 -0700
                Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-31 18:34 -0400
                Re: Sudoku Arnaud Delobelle <arnodel@gmail.com> - 2013-03-31 23:59 +0100
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-31 15:03 -0700
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-31 15:27 -0700
                Re: Sudoku Chris Angelico <rosuav@gmail.com> - 2013-04-01 09:35 +1100
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-31 20:58 -0700
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-31 15:27 -0700
                Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-30 15:06 -0700
            Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-29 14:47 -0700
        Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-28 15:11 -0700
  Re: Sudoku Damien Wyart <damien.wyart@free.fr> - 2013-03-27 09:49 +0100
  Re: Sudoku Dave Angel <davea@davea.name> - 2013-03-27 05:38 -0400
  Re: Sudoku Eric Parry <joan4eric@gmail.com> - 2013-03-27 19:49 -0700

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