Here's a small subroutine that'll test for a matched pair.

FWIW, using $a and $b as variable names in non-example code can get confusing pretty fast, especially if you're writing any sort routines.

use warnings;
use strict;

our @arr_1 = qw/  1  1  2  1  1  2  2  1  2 /;
our @arr_2 = qw/ ab aa aa ab ac ac ad ac ac /;

my ( $input1, $input2 ) = ( 1, 'ab' );
my ( $input3, $input4 ) = ( 1, 'ad' );

print "test1: ", find_match ( $input1, $input2 ), "\n";
print "test2: ", find_match ( $input3, $input4 ), "\n";

#unless ( find_match ( search pair ) ) { do something }

sub find_match {
    my ( $in1, $in2 ) = @_;
    return scalar
        grep { $in1 eq $arr_1[$_] && $in2 eq $arr_2[$_] } 0..scalar @a
+rr_1 - 1;
}
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