PHP递归获取最上级和所有子级

在做PHP开发的过程中，经常会需要获取最上级或所有子级的应用场景：

获取最顶级

$list = [
    ['id'=>1,'pid'=>0,'name'=>'张飞'],
    ['id'=>2,'pid'=>1,'name'=>'张苞'],
    ['id'=>3,'pid'=>2,'name'=>'张遵'],
    ['id'=>4,'pid'=>3,'name'=>'张三'],
    ['id'=>5,'pid'=>3,'name'=>'张四'],
];

$parent = getParent($list,5);
var_dump($parent);
function getParent($list,$id){
    foreach($list as $item) if($id == $item['id']) $citem = $item; // 当前
    if(!$citem['pid']) return $citem; // 它没有上级，则它本身就是最上级 
    return getParent($list,$citem['pid']);
}

获取所有子级

$list = [
    ['id'=>1,'pid'=>0,'name'=>'张飞'],
    ['id'=>2,'pid'=>1,'name'=>'张苞'],
    ['id'=>3,'pid'=>2,'name'=>'张遵'],
    ['id'=>4,'pid'=>3,'name'=>'张三'],
    ['id'=>5,'pid'=>3,'name'=>'张四'],
];
$childs = getChilds($list,1);
var_dump($childs);
var_dump(array_column($childs,'id'));
function getChilds($list,$id){
    $childs = [];
    foreach($list as $item){
        if($id == $item['pid']){
            $childs[] = $item;
            $childs = array_merge($childs,getChilds($list,$item['id']));
        }
    }
    return $childs;
}