[Tutor] problem with circular list

[Tim Condit]

On Sun, Jul 22, 2001 at 02:17:59PM -0600, Bruce Sass wrote:
> Hi,
> 
> > I found this problem and thought it would be fun, but it's got me
> > stumped.  The full text is at
> > http://www.karrels.org/Ed/ACM/weur94p/prob_b.html .  To sum it up, there
> > is a king, an executioner, and a variable number of condemned prisoners.
> > Every year at the games, the prisoners are lined up, and starting at the
> > first prisoner, the executioner counts off syllables of a song or
> > nursery rhyme from his youth (enie, menie, miney, moe... ) and executes
> > the prisoner he stops on.  The same nursery rhyme is used for the whole
> > "game".  The last prisoner is set free.  I looked around, and found some
> > info about circular linked lists in C, but they are built using
> > pointers.  So I devised my own routine, which doesn't work. :)
> >
> > I figured for P number of prisoners, and S number of syllables,
> > something like this would work:
> 
> The way I see it...
> you have a list of prisoners,
> and an index which may point past the end of the list.
> 
> So, you may need to reduce the index by some multiple of the
> length of the list.  e.g., something along the lines of...
> 
>     while key >= len(list):
>         key = key - len(list)
> 
> Using this approach I came up with the following for the circular
> list part of the problem...
> 
> ---8<---
> class circList:
>     def __init__(self, initial=None):
>         if initial == None:
>             self.data = []
>         else:
>             self.data = initial
> 
>     def __getitem__(self, key):
>         length = len(self.data)
>         if length > 1:
>             key = key % length
>             return self.data[key]
>         elif length == 1:
>             return self.data[0]
>         else:
>             return None  # or raise an exception
> 
> if __name__ == '__main__':
>     c = circList([0,1,2,3])
>     for i in range(10):
>         print c[i],
> --->8---
> 
> Output:
> 0 1 2 3 0 1 2 3 0 1
> 
> [Getting it to work with negative indicies and slices, or having it
>  behave more like a regular list would be interesting (but not really
>  relevent to the problem)... check out the UserList module, Section
>  2 of the Library Reference and Section 3 of the Language Reference
>  for more info.]

I thought about using UserList, maybe after getting the simple case
working.. I swear, if I don't write little programs regularly, I forget
the basics.. it's pretty frustrating.  


> 
> To make circList a little nicer you should implement a "pop" and
> the "__len__" magic method, so you can do...
> 
> ---8<---
> rhyme = ["enie", "menie", "miney", "moe", "out", "you", "go"]
> p = circList(["Bob", "Carol", "Ted", "Alice"])
> number = len(p)
> length = len(rhyme)
> while number != 1:
>     p.pop(len)
>     number = number - 1
> print p[0], "gets a pardon."
> --->8---
> 
> Output:
> Alice gets a pardon.
> 
> 
> - Bruce
> 
--- end quoted text ---

Thanks for the ideas, 

-- 
Tim Condit                        Detroit NCC
800-414-5028                      Global Crossing

The plan was simple.  Unfortunately, so was Bullwinkle.