介绍STL特性，使初学者快速入门，能够在短时间内快速了解STL编程的优点。-Introduces the STL features, so that beginners get started quickly, and can quickly understand the advantages of STL programming in a short time.

implement a class called Distinct_list (in short, D_list) that maintains a group of integers. The class is expected to have the following functionalities takes user inputs and initialize its elements accordingly, 2) remove the duplicate elements, i