PHP中怎么引用生成樹結構

PHP中怎么引用生成樹結構，很多新手對此不是很清楚，為了幫助大家解決這個難題，下面小編將為大家詳細講解，有這方面需求的人可以來學習下，希望你能有所收獲。

PHP中的引用就是兩個變量指向了同一個地方，只要在變量前面增加了&符號，它就變成了一個引用

$a='aaa';
$b=&$a;
$c=&$b;
xdebug_debug_zval('a','b','c');

輸出結果是：

a: (refcount=3, is_ref=1)='aaa'
b: (refcount=3, is_ref=1)='aaa'
c: (refcount=3, is_ref=1)='aaa'

“aaa”有了三個引用 ， 并且是is_ref是引用類型，那也就意味著不管是我修改$b ，還是修改$c , "aaa"這個都會被改變

可以根據上面這個原理來把一個數據庫存儲的帶pid的逐行數據，變成一個多層級的樹狀結構

$data=array(
    array("id"=>2,"pid"=>1),
    array("id"=>3,"pid"=>1),
    array("id"=>4,"pid"=>2),
    array("id"=>5,"pid"=>2),
    array("id"=>6,"pid"=>3),
    array("id"=>7,"pid"=>3),
    array("id"=>1,"pid"=>0),
);
$refer=array();//存儲主鍵與數組單元的引用關系
//遍歷
foreach($data as $k=>$v){
    $refer[$v['id']]=&$data[$k];//為每個數組成員建立對應關系
}
//遍歷2
foreach($data as $k=>$v){
        $parent=&$refer[$v['pid']];//獲取父分類的引用
        $parent['child'][]=&$data[$k];//在父分類的children中再添加一個引用成員
}
print_r($data);

利用了一個$refer數組，時間復雜度是O(n) , 只需要單層循環，直接通過引用修改$data原數據，生成一個樹狀結構

Array
(
    [0] => Array
        (
            [id] => 2
            [pid] => 1
            [child] => Array
                (
                    [0] => Array
                        (
                            [id] => 4
                            [pid] => 2
                        )

                    [1] => Array
                        (
                            [id] => 5
                            [pid] => 2
                        )

                )

        )

    [1] => Array
        (
            [id] => 3
            [pid] => 1
            [child] => Array
                (
                    [0] => Array
                        (
                            [id] => 6
                            [pid] => 3
                        )

                    [1] => Array
                        (
                            [id] => 7
                            [pid] => 3
                        )

                )

        )

    [2] => Array
        (
            [id] => 4
            [pid] => 2
        )

    [3] => Array
        (
            [id] => 5
            [pid] => 2
        )

    [4] => Array
        (
            [id] => 6
            [pid] => 3
        )

    [5] => Array
        (
            [id] => 7
            [pid] => 3
        )

    [6] => Array
        (
            [id] => 1
            [pid] => 0
            [child] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [pid] => 1
                            [child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 4
                                            [pid] => 2
                                        )

                                    [1] => Array
                                        (
                                            [id] => 5
                                            [pid] => 2
                                        )

                                )

                        )

                    [1] => Array
                        (
                            [id] => 3
                            [pid] => 1
                            [child] => Array
                                (
                                    [0] => Array
                                        (
                                            [id] => 6
                                            [pid] => 3
                                        )

                                    [1] => Array
                                        (
                                            [id] => 7
                                            [pid] => 3
                                        )

                                )

                        )

                )

        )

)

$a='aaa';

$b=&$a;

$c=&$b;

xdebug_debug_zval('a','b','c');

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