Re: Algebraic Expansion of Binomials Using a Recursive Subroutine

I have refactored your code:

no global variables are used by your function
all formatting is done within the function
you no longer get a trailing plus sign (+)
added check on input

use warnings;
use strict;

# Get the input
print "\nEnter the power: ";
chomp(my $power = (<STDIN>));
if (($power =~ /\D/) or ($power == 0) or ($power > 9)) {
    die "Error: $power is not a positive integer less than 10";
}

# Do the work
my $result = binomial_power(1, $power, 1);

# And print it out
print "The result is: \n(x + y)^$power = $result\n";


sub binomial_power {
    my ($c, $xp, $yp) = @_;
    my $result = $c . "x^" . $xp . "y^" . ($yp - 1);
    $result =~ s/1x/x/g;
    $result =~ s/([xy])\^1/$1/g;
    $result =~ s/[xy]\^0//g;
    if ($xp > 0) {
        $result . " + " . binomial_power((($c * $xp)/$yp), ($xp-1), ($
+yp+1));
    }
    else {
        return $result;
    }
}
[download]

While I haven't eliminated the formatting regexes, I have combined a couple of them.

Please fix the spelling of "Binomals" in your title; it will help others find your code when searching.

UPDATE: changed input checking to reject power > 9, since our code does not support it.

Comment on Re: Algebraic Expansion of Binomials Using a Recursive Subroutine Download Code

Replies are listed 'Best First'.
Re^2: Algebraic Expansion of Binomials Using a Recursive Subroutine by Jim (Curate) on Jul 31, 2011 at 04:03 UTC
More refactoring… #!/usr/bin/perl use strict; use warnings; # Get the input... print "\nEnter the power (a positive integer from 1 through 33): "; chomp(my $power = (<STDIN>)); # Quietly end if there's no input... $power =~ m/\S/ or exit 1; # Validate the input... $power =~ m/^(?:[1-9]\|[12][0-9]\|3[0-3])$/ or die "$power is not a positive integer from 1 through 33\n"; # Expand the binomial... my $expansion = binomial_expansion(1, $power, 1); # ...and then print the result... print "(x + y)^$power = $expansion\n"; exit 0; sub binomial_expansion { my ($k, $x, $y) = @_; my $term = sprintf "%dx^%dy^%d", $k, $x, ($y - 1); $term =~ s/\b1(?=x)//; # Remove 1 from 1x $term =~ s/(?<=[xy])\^1(?!\d)//g; # Remove ^1 from x^1 and y^1 $term =~ s/[xy]\^0//; # Remove x^0 and y^0 return $x > 0 ? sprintf "%s + %s", $term, binomial_expansion(($k * $x) / $y, ($x - 1), ($y + 1)) : $term ; } [download]	[reply] [d/l]
Re^2: Algebraic Expansion of Binomials Using a Recursive Subroutine by Jim (Curate) on Jul 31, 2011 at 00:44 UTC
Refactoring your refactoring just a tad… `# Get the input... print "\nEnter the power (a positive integer from 1 through 9): "; chomp(my $power = (<STDIN>)); # Quietly end if there's no input... $power =~ m/\S/ or exit 1; # Validate the input... $power =~ m/^[1-9]$/ or die "$power is not a positive integer from 1 through 9\n";` [download]	[reply] [d/l]