#!/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