on Wed, 16 Apr 2003
21:02:11 PDT
> I did at first go to Google but was stymied by the massive number of
> references, and was hoping that someone could simply suggest a "best"
> algorithm. The best reference I have found so far is "Permutations by
> Interchanges" by B. R. Heath (1963) which Sedgewick claims is the
> fastest known, but finding Heath's paper was a chore. I have finally
> located it (in TIF format!) at The Oxford University Press in England.
I just looked at Knuth to see what he has to say and there is a description on
page 44. So I whipped out a quick and dirty REXX to do it. If you need this
for a much larger number of objects you may want to optimize this code.
/* REXX permutations.cmd */
item.1 = 'item 1'
item.2 = 'item 2'
item.3 = 'item 3'
/* pick first item for this pass */
do i = 1 to 3
/* pick second item for this pass */
do k = 1 to 3
if i = k then iterate
/* pick third item for this pass */
do j = 1 to 3
if i = j then iterate
if k = j then iterate
say item.i item.k item.j
end /* do j = 1 to 3 */
end /* do k = 1 to 3 */
end /* do i = 1 to 3 */
exit
--
Robert Blair
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