use strict;
use warnings;

my $author = "Cheng, Liying, Fox, Janna., and Zheng, Ying. "; 

$author =~ s/\.| and| //g;
my %hash = split (',', $author);

my @authors;

for my $key (sort keys %hash) {
    push @authors,"$hash{$key} $key";
}

$author = join(',', @authors);
print "$author\n";