程序功能主要分为3个部分，分别是对OPT、FIFO、LRU三种页面置换算法的实现。要求3部分的设计应该尽可能使用近似的实现方法。-procedures main function is divided into three parts, namely the OPT, FIFO, three pages replacement LRU algorithm implementation. Part of the three requirements should be designed as far as possible to use similar methods to achieve.