use Data::Dumper;
use strict;
use warnings;

sub edges2vertices {
	my %vertices;
  
	for my $i ( 0 .. $#_ ) {
		$vertices{$_[$i][$_]} = 1 for (0 .. $#{$_[$i]});
	}
	return sort keys %vertices;
}

my @E = ([1,2], [1,3], [2,3,7,8], [2,4], [3,4]);
my @nv= edges2vertices(@E);
print Dumper(\@nv);