PHP迭代與遞歸實現無限級分類

無限級分類是開發中常見的情況,因此本文對常見的無限極分類算法進行總結歸納.

1.循環迭代實現

 1 $arr = [
 2     1=>['id'=>1,'name'=>'父1','father'=>NULL],
 3     2=>['id'=>2,'name'=>'父2','father'=>NULL],
 4     3=>['id'=>3,'name'=>'父3','father'=>NULL],
 5     4=>['id'=>4,'name'=>'兒1-1','father'=>1],
 6     5=>['id'=>5,'name'=>'兒1-2','father'=>1],
 7     6=>['id'=>6,'name'=>'兒1-3','father'=>1],
 8     7=>['id'=>7,'name'=>'兒2-1','father'=>2],
 9     8=>['id'=>8,'name'=>'兒2-1','father'=>2],
10     9=>['id'=>9,'name'=>'兒3-1','father'=>3],
11     10=>['id'=>10,'name'=>'兒3-1-1','father'=>9],
12     11=>['id'=>11,'name'=>'兒1-1-1','father'=>4],
13     12=>['id'=>12,'name'=>'兒2-1-1','father'=>7],
14 ];
15 function generateTree($items){
16     $tree = array();
17     foreach($items as $item){
18         if(isset($items[$item['father']])){
19             $items[$item['father']]['son'][] = &$items[$item['id']]; 
20         }else{
21             $tree[] = &$items[$item['id']];
22         }
23     }
24     return $tree;
25 }
26 $tree = generateTree($arr);
27 print_r(json_encode($tree));

輸出:

分析:

這個算法利用了循環迭代,將線性結構按照父子關系以樹形結構輸出,算法的關鍵在於使用了引用.

優點:速度快,效率高.

缺點:數組的key值必須與id值相同,不便於取出數據(使用遞歸獲取數據)

2.遞歸實現

$arr = [
    0=>['id'=>1,'name'=>'父1','father'=>0],
    1=>['id'=>2,'name'=>'父2','father'=>0],
    2=>['id'=>3,'name'=>'父3','father'=>0],
    3=>['id'=>4,'name'=>'兒1-1','father'=>1],
    4=>['id'=>5,'name'=>'兒1-2','father'=>1],
    5=>['id'=>6,'name'=>'兒1-3','father'=>1],
    6=>['id'=>7,'name'=>'兒2-1','father'=>2],
    7=>['id'=>8,'name'=>'兒2-1','father'=>2],
    8=>['id'=>9,'name'=>'兒3-1','father'=>3],
    9=>['id'=>10,'name'=>'兒3-1-1','father'=>9],
    10=>['id'=>11,'name'=>'兒1-1-1','father'=>4],
    11=>['id'=>12,'name'=>'兒2-1-1','father'=>7],
];
function generateTree($arr,$id,$step){
    static $tree=[];
    foreach($arr as $key=>$val) {
        if($val['father'] == $id) {
            $flg = str_repeat('└―',$step);
            $val['name'] = $flg.$val['name'];
            $tree[] = $val;
            generateTree($arr , $val['id'] ,$step+1);
        }
    }
    return $tree;
}
$tree = generateTree($arr,0,0);
foreach ($tree as $val){
    echo $val['name'].'<br>';
}

 

 輸出:

分析:

利用了遞歸,數組的key值與id值可以不相同,最后以順序的結構輸出數組

優點:方便遍歷,查找父子元素

缺點:php不擅長遞歸,數據量大的情況下效率會顯著降低