Here is my first try:

#!/usr/bin/perl
use File::Find;
my ( %h, $k, $d );
find(
    sub {
        $h{$File::Find::name} = 0 if -d $_;
        $h{$File::Find::dir}++ if -f _;
    },
    $ARGV[0]
);
chdir $ARGV[0];
!$h{$_} ? $d += rmdir: $k++ for ( sort { length($b) <=> length($a) } k
+eys %h );
print "Deleted $d directories, kept $k directories\n";
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