PHP中怎么引用生成树结构

PHP中怎么引用生成树结构，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。

PHP中的引用就是两个变量指向了同一个地方，只要在变量前面增加了&符号，它就变成了一个引用

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

输出结果是：

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

"aaa"有了三个引用 ， 并且是is_ref是引用类型，那也就意味着不管是我修改$b ，还是修改$c , "aaa"这个都会被改变

可以根据上面这个原理来把一个数据库存储的带pid的逐行数据，变成一个多层级的树状结构

$data=array(    array("id"=>2,"pid"=>1),    array("id"=>3,"pid"=>1),    array("id"=>4,"pid"=>2),    array("id"=>5,"pid"=>2),    array("id"=>6,"pid"=>3),    array("id"=>7,"pid"=>3),    array("id"=>1,"pid"=>0),);$refer=array();//存储主键与数组单元的引用关系//遍历foreach($data as $k=>$v){    $refer[$v['id']]=&$data[$k];//为每个数组成员建立对应关系}//遍历2foreach($data as $k=>$v){        $parent=&$refer[$v['pid']];//获取父分类的引用        $parent['child'][]=&$data[$k];//在父分类的children中再添加一个引用成员}print_r($data);

利用了一个$refer数组，时间复杂度是O(n) , 只需要单层循环，直接通过引用修改$data原数据，生成一个树状结构

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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