First of all indexing in perl starts with 0 not 1.

Then the solution is much easier than your description.

It's most likely a artificial exercise for homework, since an index like 12 is out of boundary and would make it break.

Sorry we don't run a homework service here!!!

But we give advice... looping over a reversed @a gives you the rows in the order you need....

So plz try to show us some code now! :)

UPDATE: And your example is not consistent, first you start indexing from 1 and then from 0... it's 4-2-109-