#!/usr/bin/perl -w
use strict;
use Data::Dump qw(pp);

my %country_2_name;
my %name_2_country;

while (<DATA>)
{
   s/\s*$//;  # trim trailing spaces (also chomps)
   
   my ($name, $countries) = split(' ',$_,2);   
   my @these_countries = split(/,/,$countries); 
   
   $name_2_country{$name} = [@these_countries];
   
   foreach my $this_country (@these_countries)
   {
      push @{$country_2_name{$this_country}}, $name; 
   }   
}

pp \%country_2_name;
pp \%name_2_country;

=prints
{
  Amsterdam => ["Name4"],
  Canada    => ["Name1", "Name2", "Name3", "Name5"],
  China     => ["Name3"],
  HongKong  => ["Name3"],
  India     => ["Name2", "Name5"],
  Ireland   => ["Name4"],
  London    => ["Name4"],
  Portugal  => ["Name2"],
  USA       => ["Name1", "Name4", "Name5"],
  Yemen     => ["Name1"],
}
{
  Name1 => ["USA", "Canada", "Yemen"],
  Name2 => ["Canada", "Portugal", "India"],
  Name3 => ["China", "HongKong", "Canada"],
  Name4 => ["London", "Amsterdam", "Ireland", "USA"],
  Name5 => ["India", "USA", "Canada"],
}
=cut

__DATA__
Name1  USA,Canada,Yemen 
Name2  Canada,Portugal,India
Name3  China,HongKong,Canada
Name4  London,Amsterdam,Ireland,USA
Name5  India,USA,Canada