The content of this article is about the method of realizing Infinitus classification in PHP: the recursive method and the reference method, which have certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
During the interview, I was asked about the design and implementation of Infinitus classification. A common practice is to add a PID field to distinguish the classification to which you belong when creating a table.
The data is in The storage in the database looks like this. How to implement infinite recursion? There are two common methods, recursion and reference algorithm
Recursive algorithm
/**
* 递归实现无限极分类
* @param $array 分类数据
* @param $pid 父ID
* @param $level 分类级别
* @return $list 分好类的数组 直接遍历即可 $level可以用来遍历缩进
*/
function getTree($array, $pid =0, $level = 0){
//声明静态数组,避免递归调用时,多次声明导致数组覆盖
static $list = [];
foreach ($array as $key => $value){
//第一次遍历,找到父节点为根节点的节点 也就是pid=0的节点
if ($value['pid'] == $pid){
//父节点为根节点的节点,级别为0，也就是第一级
$value['level'] = $level;
//把数组放到list中
$list[] = $value;
//把这个节点从数组中移除,减少后续递归消耗
unset($array[$key]);
//开始递归,查找父ID为该节点ID的节点,级别则为原级别+1
getTree($array, $value['id'], $level+1);
}
}
return $list;
}
/*
* 获得递归完的数据,遍历生成分类
*/
$array = getTree($array);
foreach($array) as $value{
echo str_repeat('--', $value['level']), $value['name'].'<br />';
}
//输出结果 无限极分类实现ok
河北省
--邯郸市
----永年区
--武安市
北京市
--朝阳区
----望京
----酒仙桥
--通州区Quote algorithm
function generateTree($array){
//第一步 构造数据
$items = array();
foreach($array as $value){
$items[$value['id']] = $value;
}
//第二部 遍历数据 生成树状结构
$tree = array();
foreach($items as $key => $value){
if(isset($items[$item['pid']])){
$items[$item['pid']]['son'][] = &$items[$key];
}else{
$tree[] = &$items[$key];
}
}
return $tree;
}
//经过第一步 数据变成了这样
Array
(
[1] => Array
(
[id] => 1
[pid] => 0
[name] => 河北省
[children] => Array
(
)
)
[2] => Array
(
[id] => 2
[pid] => 0
[name] => 北京市
[children] => Array
(
)
)
[3] => Array
(
[id] => 3
[pid] => 1
[name] => 邯郸市
[children] => Array
(
)
)
[4] => Array
(
[id] => 4
[pid] => 2
[name] => 朝阳区
[children] => Array
(
)
)
[5] => Array
(
[id] => 5
[pid] => 2
[name] => 通州区
[children] => Array
(
)
)
[6] => Array
(
[id] => 6
[pid] => 4
[name] => 望京
[children] => Array
(
)
)
[7] => Array
(
[id] => 7
[pid] => 4
[name] => 酒仙桥
[children] => Array
(
)
)
[8] => Array
(
[id] => 8
[pid] => 3
[name] => 永年区
[children] => Array
(
)
)
[9] => Array
(
[id] => 9
[pid] => 1
[name] => 武安市
[children] => Array
(
)
)
)
//第一步很容易就能看懂，就是构造数据，现在咱们仔细说一下第二步
$tree = array();
//遍历构造的数据
foreach($items as $key => $value){
//如果pid这个节点存在
if(isset($items[$value['pid']])){
//把当前的$value放到pid节点的son中 注意 这里传递的是引用 为什么呢？
$items[$value['pid']]['son'][] = &$items[$key];
}else{
$tree[] = &$items[$key];
}
}
//这个方法的核心在于引用，php变量默认的传值方式是按指传递
//也就是说 假如说 遍历顺序是 河北省 邯郸市 当遍历到河北省时 会把河北省放到tree中 遍历到邯郸市时 会把邯郸市放到河北省的子节点数组中 但是！！！ 这会儿的tree数组中 河北省已经放进去了 根据php变量按值传递的规则 你并没有更改tree数组中的河北省的数据 所以这里用到了引用传递
//当你对河北省做更改时，tree数组中的河北省也一并做了更改 下面我们做个实验 我们把引用传递去掉，看一下结果
//使用普通传值输出结果
Array
(
[0] => Array
(
[id] => 1
[pid] => 0
[name] => 河北省
)
[1] => Array
(
[id] => 2
[pid] => 0
[name] => 北京市
)
)
//可以看到 只有河北省和北京市输出出来了 因为他们俩是第一级节点 而且排行1和2，放到$tree数组中之后，没有使用引用传递，那么后续对他俩的子节点的操作都没有在$tree中生效，现在我们更改一下顺序 把邯郸市放到河北省的前面 那么根据咱们的推断 那么邯郸市就应该出现在tree数组里
//邯郸市放到河北省前面的输出结果
Array
(
[0] => Array
(
[id] => 1
[pid] => 0
[name] => 河北省
[son] => Array
(
[0] => Array
(
[id] => 3
[pid] => 1
[name] => 邯郸市
)
)
)
[1] => Array
(
[id] => 2
[pid] => 0
[name] => 北京市
)
)
//果然是这样 那么证明我们的推断是正确的 现在我们把引用传值改回去 再看一下
//使用引用传值输出结果
Array
(
[1] => Array
(
[id] => 1
[pid] => 0
[name] => 河北省
[children] => Array
(
[0] => Array
(
[id] => 3
[pid] => 1
[name] => 邯郸市
[children] => Array
(
[0] => Array
(
[id] => 8
[pid] => 3
[name] => 永年区
)
)
)
[1] => Array
(
[id] => 9
[pid] => 1
[name] => 武安市
)
)
)
[2] => Array
(
[id] => 2
[pid] => 0
[name] => 北京市
[children] => Array
(
[0] => Array
(
[id] => 4
[pid] => 2
[name] => 朝阳区
[children] => Array
(
[0] => Array
(
[id] => 6
[pid] => 4
[name] => 望京
)
[1] => Array
(
[id] => 7
[pid] => 4
[name] => 酒仙桥
)
)
)
[1] => Array
(
[id] => 5
[pid] => 2
[name] => 通州区
)
)
)
)
//树状结构完美的输出出来了 这个方法的核心就是引用传值Related recommendations:
php implements infinite classification tree without recursion
PHP MySQL implementation Methods for unlimited classification columns, _PHP tutorial
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