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