package PascalsTriangle;
use strict;
use warnings;
use Exporter qw<import>;
our @EXPORT_OK = qw<pascal_rows>;

sub pascal_rows {
  my ($rows) = @_;
  my $output = '';
  my @triangle = ();
  return $output unless $rows;
  return '1' if ( $rows == 1 );
  push @triangle => [ 1 ];
  foreach my $r ( 2 .. $rows) {
      my @row = ();
      foreach my $element ( 1 .. $r ) {
          my $p1 = $element == 1  ? 0 : $triangle[$r-2][$element-2];
          my $p2 = $element == $r ? 0 : $triangle[$r-2][$element-1];
          push @row => $p1 + $p2; 
      }
      push @triangle => \@row;
  }
  $output = join( "\n", map { join ' ', @$_ } @triangle );
  return $output;
}

1;