从前序与中序遍历序列构造二叉树

class TreeNode:
    def __init__(____):
        self.val = val
        self.left = left
        self.right = right

def solve():
    def buildTree(____):
        if not preorder or not inorder:
            return None
        root_val = preorder[____]
        root = TreeNode(____)
        mid = inorder.index(____)
        root.left = buildTree(____)
        root.right = buildTree(____)
        return root
    result = buildTree(____)
    print(____)