问题描述

https://leetcode.cn/problems/binary-tree-preorder-traversal/description/

解题思路

二叉树的先序遍历，没啥好说的。中-左-右。 先序中序后序 说的是中在哪里。

代码

# 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: Optional[TreeNode]) -> List[int]:
        res = []
        def dfs(root):
            if root is None:
                return
            res.append(root.val)
            dfs(root.left)
            dfs(root.right)
        dfs(root)
        return res