Sudoku
Eric Parry
joan4eric at gmail.com
Fri Mar 29 01:07:27 EDT 2013
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.
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