use strict;
use warnings;
use Time::HiRes 'time';

my @tokens = ('aaa'...'zzz');
my $start  = time;

sub build_regex {
    my ($token) = @_;
    chop $token;
    $token .= 'a';
}

my %result;

foreach my $token ( @tokens ) {
    my $regex = build_regex($token);
    my @line_results = grep { $_ ne $token and /$regex/ } @tokens;
    $result{$token} = \@line_results if @line_results;
};

printf "duration: %0.03f seconds\n", time - $start;
print scalar(keys %result), "\n"; # 16900