迭代与递归实现无限级分类

无限级分类是开发中常见的情况了,在这里我收藏了下并整理了下常见的无限极分类算法总结归纳.

<?php
$arr = [
1=>['id'=>1,'name'=>'家居','father'=>NULL],
2=>['id'=>2,'name'=>'服装','father'=>NULL],
3=>['id'=>3,'name'=>'护肤品','father'=>NULL],
4=>['id'=>4,'name'=>'生活日用','father'=>1],
5=>['id'=>5,'name'=>'家庭装修','father'=>1],
6=>['id'=>6,'name'=>'厨房卫浴','father'=>1],
7=>['id'=>7,'name'=>'男装','father'=>2],
8=>['id'=>8,'name'=>'女装','father'=>2],
9=>['id'=>9,'name'=>'面部护肤','father'=>3],
10=>['id'=>10,'name'=>'补水保湿','father'=>9],
11=>['id'=>11,'name'=>'收纳用品','father'=>4],
12=>['id'=>12,'name'=>'牛仔裤','father'=>7],
];
function generateTree($items){
$tree = array();
foreach($items as $item){
if(isset($items[$item['father']])){
$items[$item['father']]['son'][] = &$items[$item['id']];
}else{
$tree[] = &$items[$item['id']];
}
}
return $tree;
}
$tree = generateTree($arr);
print_r($tree);
?>

输出：

Array
(
[0] => Array
(
[id] => 1
[name] => 家居
[father] =>
[son] => Array
(
[0] => Array
(
[id] => 4
[name] => 生活日用
[father] => 1
[son] => Array
(
[0] => Array
(
[id] => 11
[name] => 收纳用品
[father] => 4
)

)

)

[1] => Array
(
[id] => 5
[name] => 家庭装修
[father] => 1
)

[2] => Array
(
[id] => 6
[name] => 厨房卫浴
[father] => 1
)

)

)

[1] => Array
(
[id] => 2
[name] => 服装
[father] =>
[son] => Array
(
[0] => Array
(
[id] => 7
[name] => 男装
[father] => 2
[son] => Array
(
[0] => Array
(
[id] => 12
[name] => 牛仔裤
[father] => 7
)

)

)

[1] => Array
(
[id] => 8
[name] => 女装
[father] => 2
)

)

)

[2] => Array
(
[id] => 3
[name] => 护肤品
[father] =>
[son] => Array
(
[0] => Array
(
[id] => 9
[name] => 面部护肤
[father] => 3
[son] => Array
(
[0] => Array
(
[id] => 10
[name] => 补水保湿
[father] => 9
)

)

)

)

)

)

分析:

这个算法利用了循环迭代,将线性结构按照父子关系以树形结构输出,算法的关键在于使用了引用.

优点:速度快,效率高.

缺点:数组的key值必须与id值相同,不便于取出数据(使用递归获取数据)

我们再看下递归的实现：

<?php
$arr = [
1=>['id'=>1,'name'=>'家居','father'=>NULL],
2=>['id'=>2,'name'=>'服装','father'=>NULL],
3=>['id'=>3,'name'=>'护肤品','father'=>NULL],
4=>['id'=>4,'name'=>'生活日用','father'=>1],
5=>['id'=>5,'name'=>'家庭装修','father'=>1],
6=>['id'=>6,'name'=>'厨房卫浴','father'=>1],
7=>['id'=>7,'name'=>'男装','father'=>2],
8=>['id'=>8,'name'=>'女装','father'=>2],
9=>['id'=>9,'name'=>'面部护肤','father'=>3],
10=>['id'=>10,'name'=>'补水保湿','father'=>9],
11=>['id'=>11,'name'=>'收纳用品','father'=>4],
12=>['id'=>12,'name'=>'牛仔裤','father'=>7],
];
function generateTree($arr,$id,$step){
static $tree=[];
foreach($arr as $key=>$val) {
if($val['father'] == $id) {
$flag = str_repeat('└―',$step);
$val['name'] = $flag.$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>';
}
?>

输出：

家居
└―生活日用
└―└―收纳用品
└―家庭装修
└―厨房卫浴
服装
└―男装
└―└―牛仔裤
└―女装
护肤品
└―面部护肤
└―└―补水保湿

分析:

利用了递归,数组的key值与id值可以不相同,最后以顺序的结构输出数组

优点:方便遍历,查找父子元素

缺点:php不擅长递归,数据量大的情况下效率会显著降低
总结：两种方法各有利弊，后者不适合大数据下使用，前者推荐吧