二叉树的前序中序后序代码

以下是Python实现二叉树前序、中序、后序遍历的代码：

# 定义二叉树节点类
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

# 前序遍历
def preorderTraversal(root: TreeNode) -> List[int]:
    res = []
    def dfs(node):
        if not node:
            return
        res.append(node.val)
        dfs(node.left)
        dfs(node.right)
    dfs(root)
    return res

# 中序遍历
def inorderTraversal(root: TreeNode) -> List[int]:
    res = []
    def dfs(node):
        if not node:
            return
        dfs(node.left)
        res.append(node.val)
        dfs(node.right)
    dfs(root)
    return res

# 后序遍历
def postorderTraversal(root: TreeNode) -> List[int]:
    res = []
    def dfs(node):
        if not node:
            return
        dfs(node.left)
        dfs(node.right)
        res.append(node.val)
    dfs(root)
    return res