C#搜索文件夹

要求是:
    
     在一个文件个数非常大的情况下,做快速搜索.
     文件夹存储结构:
                  第一层为文件夹名称为日期如:20100323
                                             20100322
                                             20200321
                                             .......
                  第二层文件夹名称为:某人的名称,就是在每个日期文件下都有的文件夹.名称如:张三
                                                                                        李四
                                                                                        王五
                  第三层文件夹名称为数字和名称如: 1
                                                  2
                                                  3
                                                  4
                                                  tab
                 在第三层文件夹下存储了巨量的文件.现在的要求是单独将tab文件夹拷贝出来.
如何实现高效率算法.
请各位高手帮助解答一下.给个思路便可,有代码更好了,C#,C++都可以