# some are shared by others...
@array1 = (1 .. 100001);
@array2 = (100001 .. 200001);
@array3 = (200001 .. 300000);

for $i ( 1 .. 100000, 1 .. 10000 ) 
{
    $a = int( rand( 3 ) ) + 1;
    # dark magic, beware...
    push @array4, ${*{"array$a"}}[$i];
}

my %which; 
do { push @{ $which{$_} } => "array1" } for @array1;
do { push @{ $which{$_} } => "array2" } for @array2;
do { push @{ $which{$_} } => "array3" } for @array3;

my @pairs = @array4;
while (my ($one,$two) = splice(@pairs,0,2)) {
   print "." if "$one and $two are in (@{$which{$one}}) and (@{$which{$two}}) respectively\n";
}

__END__

This renders (on my box):
4.05user 0.15system 0:04.31elapsed 97%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+22995minor)pagefaults 0swaps