伸展树的python实现

我的代码片:https://code.csdn.net/snippets_manage

# 定义顶点class Vertex:    def __init__(self, key, sum, left, right, parent):        (self.key, self.sum, self.left, self.right, self.parent) = (key, sum, left, right, parent)# 更新结点的sum属性def update(v):    if v == None:        return    # v.sum = v.key + v.left.sum + v.right.sum    v.sum = v.key + (v.left.sum if v.left != None else 0) + (v.right.sum if v.right != None else 0)    if v.left != None:        v.left.parent = v    if v.right != None:        v.right.parent = v# 左旋和右旋def smallRotation(v):    parent = v.parent    if parent == None:        return    grandparent = v.parent.parent    # 右旋    if parent.left == v:        m = v.right        v.right = parent        parent.left = m    # 左旋     else:        m = v.left        v.left = parent        parent.right = m    update(parent)    update(v)    v.parent = grandparent     if grandparent != None:        if grandparent.left == parent:            grandparent.left = v        else:             grandparent.right = v# zig-zig,zig-zagdef bigRotation(v):    if v.parent.left == v and v.parent.parent.left == v.parent:        # Zig-zig        smallRotation(v.parent)            smallRotation(v)    elif v.parent.right == v and v.parent.parent.right == v.parent:        # Zig-zig        smallRotation(v.parent)        smallRotation(v)        else:         # Zig-zag        smallRotation(v);        smallRotation(v);# 将结点v旋转至根节点        def splay(v):    if v == None:        return None    while v.parent != None:        if v.parent.parent == None:            smallRotation(v)        break        bigRotation(v)    return v# 搜索伸展树中键值为key的结点# 若结点存在,返回该结点# 若该结点不存在,返回大于该结点的最小结点# 若key对应的结点是树中的最大结点,返回Nonedef find(root, key):    v = root    last = root    next = None    while v is not None:        if v.key >= key and (next is None or v.key < next.key):            next = v        last = v        if v.key == key:            break        if v.key < key:            v = v.right        else:            v = v.left    root = splay(last)    return (next, root)# 把伸展树分割成两棵子树left,right# left子树的结点的键值均小于key,right的结点的键值均大于等于keydef split(root, key):    (result, root) = find(root, key)    if result is None:        return (root, None)    right = splay(result)    left = right.left    right.left = None    if left is not None:        left.parent = None    update(left)    update(right)    return (left, right)# 将两棵子树left和right合成一颗伸展树返回def merge(left, right):    if left is None:        return right    if right is None:        return left    while right.left is not None:        right = right.left    right = splay(right)    right.left = left    update(right)    return right# 往伸展树中插入一个结点def insert(x):    global root    (left, right) = split(root, x)    new_vertex = None    if right is None or right.key != x:        new_vertex = Vertex(x, x, None, None, None)    root = merge(merge(left, new_vertex), right)    (N, root) = find(root, x)# 删除键值为x的结点def erase(x):    global root    # Implement erase yourself    (left, right) = split(root, x)    if right is None or right.key != x:        root = merge(left, right)        return    right = right.right    if right is None:        root = merge(left, right)        return    right.parent = None    root = merge(left, right)    return