题解 | #二叉树的前序遍历#

# 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 __init__(self ):
        self.ans = []

    def pre (self, root ):
        if not root :
            return 
        self.ans.append(root.val)
        self.pre( root.left)
        self.pre(root.right)
    def preorderTraversal(self , root: TreeNode) -> List[int]:
        # write code here
        if not root:
            return []
        self.pre(root)
        return self.ans