Peter Nuttall <[EMAIL PROTECTED]> writes: > I would just write a quicksort and have a counter in the swap function. > A cunning way to do it would be to multiply the counter by -1 for each > swap. if you want I can write what I had in mind. Wikipedia has a good > article of quicksort.
Writing a sorting function from scratch for this purpose seems like reinventing the wheel. Tim's answer of simply counting the cycles (without having to pay attention to their length) is really clever. I didn't realize you could do that. Proving it is a cute exercise. Hint: any cycle of odd length has an even number of swaps, and any cycle of even length has an odd number of swaps (another exercise). http://en.wikipedia.org/wiki/Even_and_odd_permutations http://en.wikipedia.org/wiki/Permutation -- http://mail.python.org/mailman/listinfo/python-list
