preorder traversal

例句：

1. 1. Before we start the project, we need to preorder the necessary materials.
   在我们开始这个项目之前，我们需要先订购所需的材料。
2. 2. The company has implemented a preorder traversal system to improve efficiency.
   该公司已经实施了一个预购遍历系统来提高效率。
3. 3. During the preorder traversal, the customer can choose the products they want to purchase.
   在预购遍历期间，客户可以选择他们想要购买的产品。