Deele - 1 year ago 62

PHP Question

I have numbers, from 0 to 8. I would like in result, all possible sets of those numbers, each set should use all numbers, each number can occur only once in a set.

I would like to see solution made in PHP that could print out result. Or, at least, I would like some refreshment in theory of combinatorics, as I have long forgotten it. What is the formula to calculate how many permutations will there be?

Example sets:

- 0-1-2-3-4-5-6-7-8
- 0-1-2-3-4-5-6-8-7
- 0-1-2-3-4-5-8-6-7
- 0-1-2-3-4-8-5-6-7
- 0-1-2-3-8-4-5-6-7
- 0-1-2-8-3-4-5-6-7
- and so on...

Answer

You're looking for the permutations formula:

```
nPk = n!/(n-k)!
```

In your case, you have 9 entries and you want to choose all of them, that's 9P9 = 9! = 362880

You can find a PHP algorithm to permutate in recipe 4.26 of O'Reilly's "PHP Cookbook".

```
pc_permute(array(0, 1, 2, 3, 4, 5, 7, 8));
```

Copied in from O'Reilly:

```
function pc_permute($items, $perms = array( )) {
if (empty($items)) {
print join(' ', $perms) . "\n";
} else {
for ($i = count($items) - 1; $i >= 0; --$i) {
$newitems = $items;
$newperms = $perms;
list($foo) = array_splice($newitems, $i, 1);
array_unshift($newperms, $foo);
pc_permute($newitems, $newperms);
}
}
}
```

Source (Stackoverflow)