#!/usr/bin/perl   -w

# returns union, intersection and differences of two arrays
#          as per sections 14.7 and 14.8 of the Perl Cookbook
#          (but does not preserve order!)
# usage:
#  ( \@merged, \@common, \@only_a, \@only_b ) = intersets(\@a, \@b)

sub intersets {
  my ($a, $b) = @_;
  my (%ah, %bh);
  @ah{ @$a } = @$a; 
  @bh{ @$b } = ();
  delete @bh{ @$a };
  ( [ keys %ah, keys %bh ], [ grep defined, delete @ah{ @$b } ],
       [ keys %ah ], [ keys %bh ] )
}


my @a = qw(a b c d e);
my @b = qw(b e f g h i);
print "[ @a ],  [ @b ]\n
";
my($mrg, $common, $a, $b) = intersets(\@a, \@b);
print "merged: '@$mrg'\ncommon: '@$common'\n";
print "only a: '@$a'\nonly b: '@$b'\n";

=pod

[ a b c d e ],  [ b e f g h i ]

merged: 'a b c d e h i f g'
common: 'b e'
only a: 'a c d'
only b: 'h i f g'

=cut