算法：類別樹排序

Question

我已經建立了一個“無限深度”類別系統，該系統存儲在數據庫中，其中包含三個重要信息：

• 類別編號
• 父類別編號
• 的NodePath

前兩個是不言自明的，但最后一個需要澄清。 如果類別是＃20，則其父級是＃10，而父級的父級是＃5，則NodePath看起來像5:10:20 。 這樣，我可以遞歸地找到一個類別的父分支。

我正在尋找一種從數據庫中獲取每個類別的方法，然后以某種方式對它們進行排序，結果是這樣的數組：

array(
   0 => array(
      3 => array(
         7,
         13,
      ),
      5,
   ),
   1 => array(
      6,
      9
   ),
);

本質上，這是從前面描述的NodePath結構創建的樹層次結構的映射。

我想出了這樣的東西：

 $tree = array();

 foreach( $categories as $category )
 {
    // A NodePath Example is "1:7:13:24" where 1 is the root category,
    // 24 is the "leaf" or end node, and the other numbers are sub categories
    // in order.
    $nodes = explode( ":", $category->NodePath );

    $lastNode = &$tree;
    foreach( $nodes as $node )
    {
        // Add New Branch if not Termination
        if( !isset( $lastNode[ $node ] ) && $node != end($nodes) )
            $lastNode[ $node ] = array();

        // Recursive Addressing
        $lastNode = &$lastNode[ $node ];
    }        
 }

生成樹的var_dump() （與我的數據庫中的數據匹配）：

array (size=3)
  1 => 
    array (size=1)
      4 => null
  2 => 
    array (size=2)
      5 => 
        array (size=1)
          7 => &null
      6 => null
  3 => null

第三深度向下將終端節點設置為“＆null”，而不僅僅是“ null”。 我怎樣才能解決這個問題？

Answer 1

它僅在數組的最后一項發生，因此解決該問題的一種方法是在$categories的末尾添加一個NULL值，然后使用array_filter將其刪除：

$categories = [
    (object)['NodePath' => '1'],
    (object)['NodePath' => '1:4'],
    (object)['NodePath' => '2'],
    (object)['NodePath' => '2:5:7'],
    (object)['NodePath' => '2:6'],
    (object)['NodePath' => '3'],
    (object)['NodePath' => '2:5'],
    (object)['NodePath' => '3:1']
];

$tree = array();
$categories[] = (object)array('NodePath' => NULL);
foreach( $categories as $category ){
   $nodes = explode( ":", $category->NodePath );
   $lastNode = &$tree;
   foreach( $nodes as $node ){
       // Add New Branch if not Termination
       if( !isset( $lastNode[ $node ] ) && $node != end($nodes) ){
           $lastNode[ $node ] = array();
       }
       // Recursive Addressing
       $lastNode = &$lastNode[ $node ];
   }        
}
$tree = array_filter($tree);
var_dump($tree);

這是轉儲，沒有執行我所說的&在最后一個值之前。 我還嘗試過重新排列Categories數組中的元素，並且效果相同。

array(3) { [1]=> array(1) { [4]=> NULL } [2]=> array(2) { [5]=> array(1) { [7]=> NULL } [6]=> NULL } [3]=> array(1) { [1]=> NULL } } 

Answer 2

<?php


function builTree($categories){
    $tree = array();
    foreach($categories as $category){
        $path = explode( ":", $category->NodePath );
        $lastNode = &$tree;
        for($deep=0;$deep<count($path);$deep++){
             if(!is_array($lastNode[$path[$deep]])) {
                 if($deep==count($path)-1) { $lastNode[$path[$deep]] = null;}
                 else {$lastNode[$path[$deep]] = array(); $lastNode = &$lastNode[$path[$deep]];}
             } else {$lastNode = &$lastNode[$path[$deep]];}
        }
    }
    return $tree;
}


echo "<pre>";
// works with full tree given
$categories = [
    (object)['NodePath' => '1'],
    (object)['NodePath' => '1:4'],
    (object)['NodePath' => '2'],
    (object)['NodePath' => '2:5:7:90:23'],
    (object)['NodePath' => '2:6'],
    (object)['NodePath' => '3'],
    (object)['NodePath' => '2:5'],
    (object)['NodePath' => '3:1']     // even works with loop paths
];
print_r(builTree($categories));


// works even if just leafs are given
$categories = [
(object)['NodePath' => '2:5:7:90:23'],
(object)['NodePath' => '2:5:7:66:21']
];
print_r(builTree($categories));