PHP树形结构遍历：如何高效查找所有根节点及其子节点？

<?php
$tree = [
    ['node' => 2, 'children' => [3, 9, 4]],
    ['node' => 7, 'children' => [2]],
    ['node' => 3, 'children' => [6]],
    ['node' => 4, 'children' => [5]],
    ['node' => 5, 'children' => [8]],
    ['node' => 10, 'children' => [11]]
];

// 收集所有子节点
$children = [];
foreach ($tree as $v) {
    $children = array_merge($children, $v['children']);
}

// 识别根节点
$roots = [];
foreach ($tree as $item) {
    if (!in_array($item['node'], $children)) {
        $roots[] = $item['node'];
    }
}

// 递归查找子树
function findSubtree(&$tree, $roots) {
    static $result = [];
    $result = array_merge($result, $roots);

    if ($tree) {
        $nextRoots = [];
        foreach ($tree as $k => $item) {
            if (in_array($item['node'], $roots)) {
                $nextRoots = array_merge($nextRoots, $item['children']);
                unset($tree[$k]); //移除已访问节点
            }
        }
        return findSubtree($tree, $nextRoots);
    } else {
        return $result;
    }
}

$result = findSubtree($tree, $roots);
print_r($result); // 输出所有根节点及其子节点
?>