用python将二叉搜索树转换为双向循环链表，防止循环输出，再分别按正序和反序输出链表元素

好的，我来回答你的问题。

下面是将二叉搜索树转换为双向循环链表的Python代码：

class Node:
    def __init__(self, val=None, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def treeToDoublyList(root: Node) -> Node:
    if not root:
        return None

    def dfs(node):
        if not node:
            return
        dfs(node.left)
        if dfs.prev:
            dfs.prev.right = node
            node.left = dfs.prev
        else:
            dfs.head = node
        dfs.prev = node
        dfs(node.right)

    dfs.prev = None
    dfs.head = None
    dfs(root)
    dfs.head.left = dfs.prev
    dfs.prev.right = dfs.head
    return dfs.head

接下来，我们可以分别按正序和反序输出链表元素，如下：

def printList(head: Node):
    if not head:
        return
    curr = head
    while curr:
        print(curr.val, end=' ')
        curr = curr.right
        if curr == head:
            break

def printListReverse(head: Node):
    if not head:
        return
    curr = head.left
    while curr:
        print(curr.val, end=' ')
        curr = curr.left
        if curr == head.left:
            break

完整的代码如下：

class Node:
    def __init__(self, val=None, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def treeToDoublyList(root: Node) -> Node:
    if not root:
        return None

    def dfs(node):
        if not node:
            return
        dfs(node.left)
        if dfs.prev:
            dfs.prev.right = node
            node.left = dfs.prev
        else:
            dfs.head = node
        dfs.prev = node
        dfs(node.right)

    dfs.prev = None
    dfs.head = None
    dfs(root)
    dfs.head.left = dfs.prev
    dfs.prev.right = dfs.head
    return dfs.head

def printList(head: Node):
    if not head:
        return
    curr = head
    while curr:
        print(curr.val, end=' ')
        curr = curr.right
        if curr == head:
            break

def printListReverse(head: Node):
    if not head:
        return
    curr = head.left
    while curr:
        print(curr.val, end=' ')
        curr = curr.left
        if curr == head.left:
            break

# 测试代码
root = Node(4)
root.left = Node(2)
root.right = Node(5)
root.left.left = Node(1)
root.left.right = Node(3)

head = treeToDoublyList(root)
printList(head)  # 1 2 3 4 5
print()

printListReverse(head)  # 5 4 3 2 1
print()

希望能够帮助到你！