二叉树和N叉树的前序遍历

二叉树：

class Solution:
    def preorderTraversal(self, root: TreeNode) -> List[int]:
        if not(root):
            return []
        stack = [root]
        res = []
        while(stack):
            cur_node = stack.pop()
            res.append(cur_node.val)
            if cur_node.right:
                stack.append(cur_node.right)
            if cur_node.left:
                stack.append(cur_node.left)
        return res

N插树类似，只不过加入时从孩子列表的最后向前加

class Solution:
    def preorder(self, root: 'Node') -> List[int]:
        if not(root):
            return []
        stack = [root]
        res = []
        while(stack):
            cur_node = stack.pop()
            res.append(cur_node.val)
            for child in cur_node.children[::-1]:
                if child:
                    stack.append(child)
        return res