Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #42225

Re: Sudoku

Show key headers only | View raw

On Friday, March 29, 2013 9:58:27 AM UTC+10:30, Dave Angel wrote:
> On 03/28/2013 06:11 PM, Eric Parry wrote:
> 
> > On Thursday, March 28, 2013 3:06:02 PM UTC+10:30, Dave Angel wrote:
> 
> 
> 
> 
> 
>     <SNIP>
> 
> >>
> 
> >>
> 
> >> Are you familiar with recursion?  Notice the last line in the function
> 
> >> r() calls the function r() inside a for loop.
> 
> >>
> 
> >> So when r() returns, you're back inside the next level up of the
> 
> >> function, and doing a "backtrack."
> 
> >>
> 
> >> When the function succeeds, it will be many levels of recursion deep.
> 
> >> For example, if the original pattern had 30 nonzero items in it, or 51
> 
> >> zeroes, you'll be 51 levels of recursion when you discover a solution.
> 
> >>
> 
> >> If you don't already understand recursion at all, then say so, and one
> 
> >> or more of us will try to explain it in more depth.
> 
> >>
> 
>        <SNIP>
> 
> >
> 
> > 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.
> 
> > Eric.
> 
> >
> 
> 
> 
> Recursion is not limited to Python.  It's a general programming term, 
> 
> and indeed applies in other situations as well.  Suppose you wanted to 
> 
> explain what the -r switch meant in the cp command.  "r" stands for 
> 
> recursion.
> 
> 
> 
> (example is from Linux.  But if you're more familiar with Windows, it's 
> 
> the /s switch in the DIR command.)
> 
> 
> 
> The cp command copies all the matching files in one directory to another 
> 
> one.  If the -r switch is specified, it then does the same thing to each 
> 
> subdirectory.
> 
> 
> 
> Notice we did NOT have to specify sub-subdirectories, since they're 
> 
> recursively implied by the first description.
> 
> 
> 
> 
> 
> Closer to the current problem, suppose you defined factorial in the 
> 
> following way:  factorial(0) is 1, by definition.  And for all n>0, 
> 
> factorial(n) is n*factorial(n-1).
> 
> 
> 
> So to directly translate this definition to code, you write a function 
> 
> factorial() which takes an integer and returns an integer.  If the 
> 
> parameter is zero, return one.  If the parameter is bigger than zero, 
> 
> then the function calls itself with a smaller integer, building up the 
> 
> answer as needed  (untested).
> 
> 
> 
> def  factorial(n):
> 
>      if n==0:
> 
>          return 1
> 
>      val = n *factorial(n-1)
> 
>      return val
> 
> 
> 
> 
> 
> 
> 
> 
> 
> -- 
> 
> DaveA

Thank you for that Dave, I've started writing the VBA code.
Eric.

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

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

csiph-web