diamondsandperls:

He means logic like:

my %seen;
for my $key (0 1 2 1 2 3 2 3 4 3 4 5) {
  print $key unless $seen{$key}++;
}
[download]

This (untested) script should just print the values 0 through 5 in order. The $key value is just the data you use to tell whether it's identical or not. When you first check the %seen hash for the value 0, there won't be an entry for zero, so the print will execute. The line also increments the value in the %seen hash to 1, so the next time you see 0 it *won't* print.

You just need the %seen hash, the data you use for the $key, and an action you want to control.

...roboticus

When your only tool is a hammer, all problems look like your thumb.