This uses an array slice greping the indices of @b that satisfy the criteria.

use strict;
use warnings;

my @a = ( 1, 9, 3, 4, 5, 6, 7, 2, 4, 3 );
my @b = qw{ x y z z a z z z b c };

my @aNew = @a[ grep {
                        ! $_
                        ||
                        $b[ $_ ] ne q{z}
                        ||
                        $b[ $_ - 1 ] ne q{z}
                    } 0 .. $#b ];
print qq{@aNew};
[download]

The output.

1 9 3 5 6 4 3
[download]

I hope this is of interest.

Cheers,

JohnGG