我的代码中出现了一个错误。问题:从预序和中序遍历构造二叉树

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def buildTree(preorder, inorder):
    if not preorder or not inorder:
        return None
    
    root_val = preorder[0]
    root = TreeNode(root_val)
    
    root_index = inorder.index(root_val)
    
    left_inorder = inorder[:root_index]
    right_inorder = inorder[root_index+1:]
    
    left_preorder = preorder[1:1+len(left_inorder)]
    right_preorder = preorder[1+len(left_inorder):]
    
    root.left = buildTree(left_preorder, left_inorder)
    root.right = buildTree(right_preorder, right_inorder)
    
    return root

# 示例调用
preorder = [3,9,20,15,7]
inorder = [9,3,15,20,7]
root = buildTree(preorder, inorder)