Sudoku.class

$sud = new Sudoku($argv[1]);
$sud->solve();
$sud->printSudoku();

class Sudoku {
    public $charset = array(1,2,3,4,5,6,7,8,9); # = range(0,9);
    public $sudoku = array(
        'x' => 9,
        'y' => 9,
        'boxX' => 3,
        'boxY' => 3
    );
    private $sud;
    private $holes = array();
    public  $emptyHole = '.';

    function __construct($sud) {
        $this->sud = $sud;

        for($i = 0; $i < strlen($sud); $i++)
            if($sud{$i} == $this->emptyHole) $this->holes[] = $i;
    }

    private function _getHoles() {
        $this->holes = array();
        for($i = 0; $i < strlen($this->sud); $i++)
            if($this->sud{$i} == $this->emptyHole) $this->holes[] = $i;
    }

    public function solve($layer=0) {
        $possibleChars = $this->_getChars($this->holes[$layer]+1);

        foreach($possibleChars as $char) {
            $this->sud{$this->holes[$layer]} = $char;
            if($layer != count($this->holes)-1) {
                if($this->solve($layer+1)) return $this->sud;
            } else return $this->sud;
        }

        $this->sud{$this->holes[$layer]} = $this->emptyHole;
        return false;
    }

    private function _getChars($position) {
        return array_intersect($this->_checkBox(ceil((ceil($position/$this->sudoku['x']))/$this->sudoku['boxX']),ceil(($this->_checkColumn($position-(ceil($position/$this->sudoku['x']))*$this->sudoku['x']+$this->sudoku['x'])/$this->sudoku['boxY'])),$this->_checkRow(ceil($position/$this->sudoku['x'])),$this->_checkColumn($position-(ceil($position/$this->sudoku['x']))*$this->sudoku['x']+$this->sudoku['x']));
    }

    private function _checkRow($row) {
        $vorkommen = array();
        for($i = $row*$this->sudoku['x']-$this->sudoku['x']; $i < $row*$this->sudoku['x']; $i++)
            if($this->sud{$i} != '.')
                $vorkommen[] = $this->sud{$i};

        return array_diff($this->charset,$vorkommen);
    }

    private function _checkColumn($column) {
        $vorkommen = array();
        for($i = $column-1; $i < $this->sudoku['x']*$this->sudoku['y']; $i += $this->sudoku['x'])
            if($this->sud{$i} != '.')
                $vorkommen[] = $this->sud{$i};

        return array_diff($this->charset,$vorkommen);
    }

    private function _checkBox($boxrow,$boxcolumn) {
        $vorkommen = array();
        $startbox = ($boxrow*$this->sudoku['boxY']*$this->sudoku['x'])-$this->sudoku['boxY']*$this->sudoku['x']+$this->sudoku['boxY']*$boxcolumn-$this->sudoku['boxY'];

        for($a = 0; $a < $this->sudoku['boxY']; $a++) {
            for($i = 0; $i < $this->sudoku['boxX']; $i++) {
                if($this->sud{$i+$startbox} != '.')
                    $vorkommen[] = $this->sud{$i+$startbox};
                if($startbox+$this->sudoku['boxX'] === $startbox+$i+1)
                    $startbox += $this->sudoku['x'];
            }
        }

        return array_diff($this->charset,$vorkommen);
    }

    public function printSudoku($inline=false) {
        if($inline) {
            print implode('',$this->sud);
        } else {
            print "\n";
            $a = 0;
            for($i = 0; $i < strlen($this->sud); $i++) {
                print str_replace('.',$this->emptyHole,$this->sud{$i})." ";
                if(($i+1) % $this->sudoku['boxX'] === 0) print "  ";

                if(($i+1) % $this->sudoku['x'] === 0) {
                    print "\n";
                    if(($a+1) % $this->sudoku['boxY'] === 0) print "\n";

                    $a++;
                }
            }
        }
    }
}