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    my %b_hash = map { $_ => 1 } @b_array;
    my @new_array = grep $b_hash{$_}, @a_array;

    my %b_hash;
       $b_hash {$_} ++ for @b_array;
    my @c_array = map {($_) x ($b_hash {$_} || 0)} @a_array;