OK, This is the code :

#!/usr/bin/perl -w

use strict;


my %stuff;

while(<DATA>)
{
   chomp;

   my ( $country,$state,$city) = split /:/;

   push @{$stuff{$country}->{$state}},$city;
}

foreach my $country ( keys %stuff )
{
   print "The states in $country are ",join ",",keys %{$stuff{$country
+}},"\n";
   foreach my $state ( keys %{$stuff{$country}} )
   {
      print "The cities in $state are ",
             join ",", @{$stuff{$country}->{$state}},"\n";
   }
}

__DATA__
USA:CA:Los Angeles
USA:CA:San Francisco
USA:NY:New York
CAN:Alb:Edmonton
CAN:Alb:Calgary
[download]

Now read perldsc and come back if you have any questions :)

/J\