It's more fun with a regular expression! ;)

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/;

# Target: @anew =(1,9,3,5,6,4,3)

my @anew = boil( \@a, \@b );

print "@anew\n";



sub boil {
    my ( $numbers, $letters ) = @_;
    my $pad = '';
    $pad .= $letters->[$_] . $numbers->[$_] foreach 0 .. $#{$numbers};
    {
        no warnings qw/uninitialized/;
        $pad =~ s/(?:z(.)(?:z.)+)|(?:.(.))/$1$2/g;
    }
    return split //, $pad;
}
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I suspect the goal isn't "fun", so bear in mind that the RE approach is fragile if your input data deviates from the format you provided. For example, double-digit numerals will pretty much be the end of the fun unless the RE is modified to accommodate that contingency. But I couldn't resist the opportunity to play with it nevertheless.