Factorial

This week we're going to delve into some discrete math, starting with factorial. The factorial of a number is the product of that number and all the numbers smaller than it. For example, the factorial of 3 is 1 x 2 x 3 = 6.

ASP

1. function factorial(x)
2.     dim result
4.     result = 1
6.     if x > 1 then
7.         for i = 2 to x
8.             result = result * i
9.         next
10.     end if
12.     factorial = result
13. end function

PHP

1. function factorial($x)
2. {
3.     $result = 1;
5.     if ($x > 1)
6.     {
7.         for ($i = 2; $i <= $x; $i++)
8.         {
9.             $result *= $i;
10.         }
11.     }
13.     return $result;
14. }

Now that we have a function for factorial, we can also do combinatorial. Combinatorial tells us the number of combinations, without regard to order, of y items that can be made from a pool of x items.

ASP

1. function combinatorial(x, y)
2.     if (x >= y) and (y > 0) then
3.         combinatorial = factorial(x) / factorial(y) / factorial(x - y)
4.     else
5.         combinatorial = 0
6.     end if
7. end function

PHP

1. function combinatorial($x, $y)
2. {
3.     return (($x >= $y) && ($y > 0)) ? factorial($x) / factorial($y) / factorial($x - $y) : 0;
4. }

We can also get the number of permutations of y items that can be made from a pool of x items.

ASP

1. function permutations(x, y)
2.     permutations = factorial(x) / factorial(x - y)
3. end function

PHP

1. function permutations($x, $y)
2. {
3.     return factorial($x) / factorial($x - $y);
4. }

• ASP implementation on Snipplr
• PHP implementation on Snipplr