Backtracking, prementions, and 8-Queens

algo.php

<?php

// http://paulbutler.org/archives/n-queens-in-a-tweet/
$n=$argv[1];$s=range(1,$n);while($i<$n*10000){shuffle($s);$a=s($s,range(1,$n));$b=s(s($s,range($n,1)),2*$n);$c=array_merge($a,$b);if(count(array_unique($c))==2*$n){die(join(',',$s));}$i++;}function s($a,$b){if(!is_array($b))$b=array_fill(0,count($a),$b);foreach($a as $i=>$k)$r[$i]=$k+$b[$i];return $r;}