給定一顆n叉樹，返回對它節點值的前序遍歷
例如，給定一個3叉樹：

返回它的前序遍歷為：[1,3,5,6,2,4]
注意：遞迴很簡單，請嘗試用迭代的方法完成

1、迭代

def preorder(self, root):
        """
        :type root: Node
        :rtype: List[int]
        """
        if not root:
            return []
        gBack = []
        nodeList = [root]
        while nodeList:
            node =
 
 nodeList.pop(0)
            if node:
                gBack.append(node.val)
                for i in node.children[::-1]:
                    nodeList.insert(0, i)
        return gBack

2、遞迴

def preorder(self, root):
        """
        :type root: Node
        :rtype: List[int]
        """
        if
 
 not root:
            return []
        gBack = [root.val]
        for node in root.children:
            gBack += self.preorder(node)
        return gBack

演算法題來自：https://leetcode-cn.com/problems/n-ary-tree-preorder-traversal/description/