题解 | #求二叉树的前序遍历#

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

#
# 
# @param root TreeNode类 
# @return int整型一维数组
#
class Solution:
    def preorderTraversal(self , root ):
        # write code here
        res = []
        
        def dfs(root):
            if not root:
                return
            res.append(root.val)
            dfs(root.left)
            dfs(root.right)
        
        dfs(root)
        return res