size = $n;
        $this->arr = array();
        $this->sol = 0;
        // Inicialiate array;
        for($i=0; $i<$n; $i++) {
            $this->arr[$i] = 0;
        }
    }

    function isSolution($n) {
        for ($i = 0; $i < $n; $i++) {
            if ($this->arr[$i] == $this->arr[$n] ||
            ($this->arr[$i] - $this->arr[$n]) == ($n - $i) ||
            ($this->arr[$n] - $this->arr[$i]) == ($n - $i))
            {
                return false;
            }
        }
        return true;
    }

    function PrintQueens() {
        echo("solution #".(++$this->sol)."\n");
        // echo("solution #".($this->size)."\n");
        for ($i = 0; $i < $this->size; $i++) {
            for ($j = 0; $j < $this->size; $j++) {
                if ($this->arr[$i] == $j) echo("& ");
                else echo(". ");
            }
            echo("\n");
        }
        echo("\n");
    }


    // backtracking Algorithm
    function run($n = 0) {
        if ($n == $this->size){
            $this->PrintQueens();
        }
        else {
            for ($i = 0; $i < $this->size; $i++) {
                $this->arr[$n] = $i;
                if($this->isSolution($n)){
                    $this->run($n+1);
                }
            }
        }
    }
}

$myprogram = new Queens(8);
$myprogram->run();

?>