- pow: documentation ( source)
- count_chars: documentation ( source)
<?php
function variations($length, $chars) {
$unique_chars = count_chars($chars, 3);
if ($length <= 0 || $unique_chars <= 0) return 0;
$additional = ($length > 1) ? variations($length - 1, $chars) : 0;
return pow($unique_chars, $length) + $additional;
}
echo variations(10, 26);