题解 | #二叉树的前序遍历#

from typing import List
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

def preorderTravelsal(root: TreeNode) -> TreeNode:
    lists = []
    preorder(lists, root)
    return lists

def preorder(list: List[int], root: TreeNode):
    if root == None:
        return None
    # 先遍历根节点
    list.append(root.val)
    # 再去左子树
    preorder(list, root.left)
    # 再去右子树
    preorder(list, root.right)

if __name__ == '__main__':
    # lists = input().split(',')
    root = TreeNode(1)
    root.left = None
    root.right = TreeNode(2)
    root.right.left = TreeNode(3)
    result = preorderTravelsal(root)
    print(result)