PHP無限級分類實現（遞歸+非遞歸）

<?php  
/** 
 * Created by PhpStorm. 
 * User: qishou 
 * Date: 15-8-2 
 * Time: 上午12:00 
 */  
//準備數組，代替從數據庫中檢索出的數據(共有三個必須字段id,name,pid)  
header("content-type:text/html;charset=utf-8");  
$categories = array(  
    array('id'=>1,'name'=>'電腦','pid'=>0),  
    array('id'=>2,'name'=>'手機','pid'=>0),  
    array('id'=>3,'name'=>'筆記本','pid'=>1),  
    array('id'=>4,'name'=>'臺式機','pid'=>1),  
    array('id'=>5,'name'=>'智能機','pid'=>2),  
    array('id'=>6,'name'=>'功能機','pid'=>2),  
    array('id'=>7,'name'=>'超級本','pid'=>3),  
    array('id'=>8,'name'=>'遊戲本','pid'=>3),  
);  
  
/*======================非遞歸實現========================*/  
$tree = array();  
//第一步，將分類id做爲數組key,並建立children單元  
foreach($categories as $category){  
    $tree[$category['id']] = $category;  
    $tree[$category['id']]['children'] = array();  
}  
//第二步，利用引用，將每一個分類添加到父類children數組中，這樣一次遍歷便可造成樹形結構。  
foreach($tree as $key=>$item){  
    if($item['pid'] != 0){  
        $tree[$item['pid']]['children'][] = &$tree[$key];//注意：此處必須傳引用不然結果不對  
        if($tree[$key]['children'] == null){  
            unset($tree[$key]['children']); //若是children爲空，則刪除該children元素（可選）  
        }  
    }  
}  
////第三步，刪除無用的非根節點數據  
foreach($tree as $key=>$category){  
    if($category['pid'] != 0){  
        unset($tree[$key]);  
    }  
}  
  
print_r($tree);  
  
/*======================遞歸實現========================*/  
$tree = $categories;  
function get_attr($a,$pid){  
    $tree = array();                                //每次都聲明一個新數組用來放子元素  
    foreach($a as $v){  
        if($v['pid'] == $pid){                      //匹配子記錄  
            $v['children'] = get_attr($a,$v['id']); //遞歸獲取子記錄  
            if($v['children'] == null){  
                unset($v['children']);             //若是子元素爲空則unset()進行刪除，說明已經到該分支的最後一個元素了（可選）  
            }  
            $tree[] = $v;                           //將記錄存入新數組  
        }  
    }  
    return $tree;                                  //返回新數組  
}  
echo "<br/><br/><br/>";  
  
print_r(get_attr($tree,0));