On Sun, 8 Nov 2009, Ozz wrote:

> 
>  Hi,
> 
>  > My first question is:
>  > 1. given a list of invoives I=[500, 400, 450, 200, 600, 700] and a
>  > check Ch=600
>  > how can I print all the different combinations of invoices that the
>  > check is possibly cancelling
> 
>  Incidentally, I'm currently learning python myself, and was working
>  on more or less the same problem as an exercise;
> 
>  For listing all different subsets of a list (This is what I came up
>  with. Can it be implemented shorter, btw?):
> 
>  def subsets(L):
>          S = []
>          if (len(L) == 1):
>                  return [L, []]
>          else:
>                  for s in subsets(L[1:]):
>                          S.append(s)
>                          S.append(s + [ L[0]])
>          return S
> 
>  Now, to use the above piece of code (after 'import subset'):
> 
>  >>> subset.subsets([4,7,8,2])
>  [[2], [2, 4], [2, 7], [2, 7, 4], [2, 8], [2, 8, 4], [2, 8, 7], [2, 8, 7, 4],
>  [], [4], [7], [7, 4], [8], [8, 4], [8, 7], [8, 7, 4]]
>  >>> map(sum,subset.subsets([4,7,8,2]))
>  [2, 6, 9, 13, 10, 14, 17, 21, 0, 4, 7, 11, 8, 12, 15, 19]
> 
>  It's not a real solution yet, and as others have pointed out the
>  problem is NP complete but it might help to get you going.

  does your solution allow for the possibility of different invoices
of equal amounts?  i would be reluctant to use the word "subset" in a
context where you can have more than one element with the same value.

rday
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Robert P. J. Day                               Waterloo, Ontario, CANADA

            Linux Consulting, Training and Kernel Pedantry.

Web page:                                          http://crashcourse.ca
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