Added a unique filter, in case the data contains duplicates:

use strict;
use warnings;
my %uniq;
my @array = sort {$a <=> $b} grep {$uniq{$_}++==0} qw/ 23 45 12 4 45 8
+ 7 5/;

while (my $item = shift @array) {
    print "$item $_\n" for @array;
}
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(the number 45 is duplicated here, but only one appears in the output).