题目描述
给你二叉树的根节点 root ,返回它节点值的 前序 遍历。
python 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]:
if not root:return[]
stack, res = [root],[]
while stack:
node = stack.pop()
if node:
res.append(node.val)#根节点值加入到结果
if node.right:#右子树入栈
stack.append(node.right)
if node.left:#左子树入栈
stack.append(node.left)
return res