my @A = (1,2,3,4,5,4,3,2,1,2);
my @B = (2,4,6,8,10,8,6,4,2);
my (%First, %Second);

push @{ $First{  $A[$_] } }, $_ for (0..$#A);
push @{ $Second{ $B[$_] } }, $_ for (0..$#B);

my %Pairs;
for my $Common (grep {exists $Second{$_}} keys %First){
  for my $Idx (@{ $First{$Common} }){
    push @{ $Pairs{$Common} }, map([$Idx, $_], @{ $Second{$Common} });
  }
}

# Print out what we found
for (sort keys %Pairs){
  print "$_:\n", map("  $_\n", map(join('-', @$_), @{ $Pairs{$_} })), "\n";
}