【20250215】二叉树：144.二叉树的前序遍历
# 前序遍历-递归-LC144_二叉树的前序遍历
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
# class Solution:
# def preorderTraversal(self, root):
# res = []
# def dfs(node):
# if node is None:
# return
# res.append(node.val)
# dfs(node.left)
# dfs(node.right)
# dfs(root)
# return res
class Solution:
def preorderTraversal(self,root):
res=[]
#dfs是指深度优先搜索
def dfs(node):
if node is None:
return
res.append(node.val)
dfs(node.left)
dfs(node.right)
dfs(root)
return res