数独 回溯算法

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数独 回溯算法，计算未填写的 九宫格

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class bord {
    private $bord;

    public function __construct(array $bord) {
        $this->bord = $bord;
    }


    public function run() {
        $pos = $this->next();
      // var_dump($pos);
        if ($pos == false) {
            return true;
        };
        list($x, $y) = $pos;
//       echo $this->string($x,$y);
//       echo '<br/>';


        for ($v = 1; $v < 10; $v++) {
          //  var_dump($x, $y, $v);
           // var_dump($this->check($x, $y, $v));
          //echo $this->__toString();
            if ($this->check($x, $y, $v)) {
                $this->set($x, $y, $v);
                if($this->run()){
                    return true;
                };

            }


        }
        $this->release($x, $y);
     //   $this->run();

        return false;




    }

    public function next() {
        foreach ($this->bord as $x => $array) {
            foreach ($array as $y => $v) {
                if ($v == 0) {
                    return [$x, $y];
                }
            }
        }
        return false;
    }

    public function check($x, $y, $v) {
        foreach ($this->bord as  $x_a) {

            if ($x_a[$y] == $v) {
                return false;
            }
        }

        foreach ($this->bord[$x] as $y_v) {
           // var_dump($y_v);
            if ($y_v == $v) {
                return false;
            }
        }

        $x_b = intval(floor(($x-1)/3)*3 +1);

        $y_b = intval(floor(($y-1)/3)*3 +1);
       // var_dump('x',$x_b);var_dump('y',$y_b);

        for ($x = $x_b; $x < $x_b + 3; $x++) {
            for ($y = $y_b; $y < $y_b + 3; $y++) {
                if($this->bord[$x][$y] ==$v){
                    return false;
                }
            }
        }

        return true;
    }

    public function set($x, $y, $v) {
        $this->bord[$x][$y] = $v;
    }

    public function complete() {
        return $this->next() === false;
    }

    public function release($x, $y) {
        $this->bord[$x][$y] = 0;
    }
    public function string($x_r=null,$y_r=null) {
        $str = '';
        foreach ($this->bord as $x => $array) {
            foreach ($array as $y => $v) {
                if($x_r && $y_r && $x_r==$x && $y_r==$y){
                    $str .= '<span style="color:red">'.$v . '</span>&nbsp; &nbsp;  ';
                }else{
                    $str .= $v . '&nbsp; &nbsp;  ';
                }


            }
            $str .= '<br/>';
        }
        return $str;

    }
    public function __toString() {
        $str = '';
        foreach ($this->bord as $x => $array) {
            foreach ($array as $y => $v) {
                    $str .= $v . '&nbsp; &nbsp;';
            }
            $str .= '<br/>';
        }
        return $str;

    }
}

$bord  = new bord(array_fill(1,9,array_fill(1,9,0)));
$bord ->run();
echo $bord ;