PHP データ構造: ツリー構造の探索、階層データの構成の習得

class Node {
  public $value;
  public $children = [];

  public function __construct($value) {
    $this->value = $value;
  }

  public function addChild(Node $child) {
    $this->children[] = $child;
  }
}

$tree = [
  'value' => 'Root',
  'children' => [
    [
      'value' => 'Child 1',
      'children' => []
    ],
    [
      'value' => 'Child 2',
      'children' => [
        'value' => 'Grandchild'
      ]
    ]
  ]
];

function traverseRecursively($node) {
  echo $node->value . PHP_EOL;
  foreach ($node->children as $child) {
    traverseRecursively($child);
  }
}

function traverseIteratively($node) {
  $stack = [$node];
  while (!empty($stack)) {
    $current = array_pop($stack);
    echo $current->value . PHP_EOL;
    foreach (array_reverse($current->children) as $child) {
      $stack[] = $child;
    }
  }
}

class Directory {
  public $name;
  public $children = [];

  public function __construct($name) {
    $this->name = $name;
  }

  public function addChild(Node $child) {
    $this->children[] = $child;
  }
}

$root = new Directory('/');

$dir1 = new Directory('dir1');
$dir2 = new Directory('dir2');
$dir3 = new Directory('dir3');

$file1 = new File('file1.txt');
$file2 = new File('file2.php');

$dir1->addChild($file1);
$dir2->addChild($file2);
$root->addChild($dir1);
$root->addChild($dir2);
$root->addChild($dir3);

traverseRecursively($root);