There are a lot of ways to use an array backwards.

One is to simply reverse the order of the sort.  For example, instead of

my @sorted = sort @unsorted;
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which is doing an implicit sort { $a cmp $b } @unsorted, you could do:

my @sorted = sort { $b cmp $a } @unsorted;
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to have the order reversed at the end of the sort.

Another way is to read an item one-at-a-time from the end of the list, such as in:

my $nextitem;
while ($nextitem = pop @rocks) {
    # Use $nextitem
}
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(Sorry, I couldn't resist using pop @rocks :-))

As a 3rd and final example, read one at a time from the end of the array using an index, using the -N notation (which reads from the -Nth value of the array each time):

for (my $i=1; $i <= @rocks; $i++) {
    my $nextitem = $rocks[- $i];    # Take the ${i}th item from the en
+d
}
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