[RickMuller]
> I have to sort a list, but in addition to the sorting, I need to
> compute a phase factor that is +1 if there is an even number of
> interchanges in the sort, and -1 if there is an odd number of
> interchanges.
It occurs to me that the previously posted comparison count won't do it.
The only idea that comes to mind is to do a selection sort and count the number
of swaps.
a = [1,10,2,7]
parity = 1
for i in xrange(len(a)-1):
x = a[i]
lowest = i
for j in xrange(i, len(a)):
if a[j] < a[lowest]:
lowest = j
if i != lowest:
a[i], a[lowest] = a[lowest], a[i]
parity = -parity
print 'swapping %d with %d. parity is %d' % (i, lowest, parity)
print parity, a
Raymond
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