Hey kiat,
I noticed that your algorithm skips the "1 1" row. I made some changes to fix that bug:

sub pascal {
  my ($rows) = @_;
  print "1\n";
  for (my $outer = 1; $outer < $rows; $outer++) {
    my $inner = $outer;
    print "1";
    for ($i = 1; $i < $inner; $i++) {
      my $denominator = factorial($i)*(factorial($inner-$i)); 
      my $pascalnum = factorial($inner)/$denominator if ($denominator 
+!= 0);
      print " $pascalnum" if ($outer > 1);
    }
    print " 1\n";
  }
}
[download]

I also think that using the Binomial Theorem when printing out an entire Pascal's triangle is inefficient. I would rather add numbers from the previous row, as this is much, much faster for large numbers of rows. So I wrote up some code to do this:

sub ton_pascal
{
    my $rows = shift;
    my $last_row = [ ];
    my $this_row = [ 1 ];
    
    last unless ($rows > 0);
    print "1\n";
    for (my $i = 1; $i < $rows; ++$i) {
        $last_row = $this_row;
        $this_row = [ 1 ];
        for (my $j = 1; $j < $i; $j++) {
            push(@$this_row, $last_row->[$j - 1] + $last_row->[$j]);
        }
        push(@$this_row, 1);
        print join(' ', @$this_row) . "\n";
    }    
}
[download]

I'm using array references instead of arrays for extra speed (when we copy the results of $this_row into $last_row), but the references could be removed without affecting the algorithm.

Hope this was helpful... I had fun coding up ton_pascal, so thanks for the problem!

-Ton
-----
Be bloody, bold, and resolute; laugh to scorn
The power of man...

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.