无限级分类是开发中常见的情况,也经常会在面试，主考官问到，笔试中遇到，因此本文对常见的无限极分类算法进行总结归纳，其实大多数就是迭代与递归。
1.循环迭代实现
$arr = [
1=>['id'=>1,'name'=>'父1','father'=>NULL],
2=>['id'=>2,'name'=>'父2','father'=>NULL],
3=>['id'=>3,'name'=>'父3','father'=>NULL],
4=>['id'=>4,'name'=>'儿1-1','father'=>1],
5=>['id'=>5,'name'=>'儿1-2','father'=>1],
6=>['id'=>6,'name'=>'儿1-3','father'=>1],
7=>['id'=>7,'name'=>'儿2-1','father'=>2],
8=>['id'=>8,'name'=>'儿2-1','father'=>2],
9=>['id'=>9,'name'=>'儿3-1','father'=>3],
10=>['id'=>10,'name'=>'儿3-1-1','father'=>9],
11=>['id'=>11,'name'=>'儿1-1-1','father'=>4],
12=>['id'=>12,'name'=>'儿2-1-1','father'=>7],
];
function generateTree($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(json_encode($tree));
输出:
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(同样使用迭代获取数据)
2.递归实现
$arr = [
0=>['id'=>1,'name'=>'父1','father'=>0],
1=>['id'=>2,'name'=>'父2','father'=>0],
2=>['id'=>3,'name'=>'父3','father'=>0],
3=>['id'=>4,'name'=>'儿1-1','father'=>1],
4=>['id'=>5,'name'=>'儿1-2','father'=>1],
5=>['id'=>6,'name'=>'儿1-3','father'=>1],
6=>['id'=>7,'name'=>'儿2-1','father'=>2],
7=>['id'=>8,'name'=>'儿2-1','father'=>2],
8=>['id'=>9,'name'=>'儿3-1','father'=>3],
9=>['id'=>10,'name'=>'儿3-1-1','father'=>9],
10=>['id'=>11,'name'=>'儿1-1-1','father'=>4],
11=>['id'=>12,'name'=>'儿2-1-1','father'=>7],
];
function generateTree($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'].'
';
}
输出
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
