某书店以文件形式保存其每一笔交易。每一

笔交易记录某本书的销售情况，含有 ISBN（国际标准书号，世界上每种图书的唯一标识符）、销售册数和销售单价。店主定

期地查看这个文件，统计每本书的销售册数、总销售收入以及平均售价的算法-A bookstore in file format each transaction. Every

Transaction record sales of a book, containing ISBN (international standard book number, the world titles in each unique identifier), the number of copies sold and sales price. The owner

During the period of viewing this document, statistics for each book sold copies, total sales income and the average selling price of algorithm