题解 | #二叉树的前序遍历（非递归）#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return int整型一维数组
#
class Solution:
    def preorderTraversal(self , root: TreeNode) -> List[int]:
        if root==None:
            return
        
        result=[]
        stack=[]
        stack.append(root)
        while stack:
            top=stack.pop()
            
            result.append(top.val)
            if top.right:
                stack.append(top.right)
            if top.left:
                stack.append(top.left) 
        return  result
            
        # write code here