Re: Perl program to generate a descending order of 9-unique digit numbers

This is, of course, doable with regex (what isn't?)

#!/usr/bin/perl
use strict; use warnings;
$\ = "\n";
$_ = 9876543210;
my $n = 0; # to limit output

$n++ < 12 or exit while print,
  s/.*\K (.) (?=(.)(??{$1 < $2 and 'x'})
  (.*) (.)(??{$1 < $4 and 'x'}) (.*)
  / $4 . reverse $3.$1.$5 /xe
[download]

Comment on Re: Perl program to generate a descending order of 9-unique digit numbers Download Code

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Re^2: Perl program to generate a descending order of 9-unique digit numbers by Anonymous Monk on Apr 26, 2016 at 15:39 UTC
Cleaned up and annotated. It's a perl version of https://en.m.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order `#!/usr/bin/perl -l use strict; use warnings; $_ = 321; # for testing, change to 987654321 for final run 1 while print, s/.\K # find the last (.) # digit such that (.) # there is a later (latest) (.)(??{$1 < $3 and 'x'}) # digit less than it (.*) # and get rest # swap those two digits ( $1 & $3 ) # then reverse everything after the first swapped digit / $3 . reverse $2.$1.$4 /xe` [download]	[reply] [d/l]
Re^2: Perl program to generate a descending order of 9-unique digit numbers by Anonymous Monk on Apr 26, 2016 at 09:16 UTC
`$_ = 987654321; # oops, 9 unique digits` [download]	[reply] [d/l]