589. N-ary Tree Preorder Traversal

Python

class Solution:
    def preorder(self, root: 'Node') -> List[int]:

        def travel(node, result):
            if not node:
                return

            result.append(node.val)
            for child in node.children:
                travel(child, result)

        result = []
        travel(root, result)
        return result