PWM 控制 LED 灯渐亮渐灭程序，有详细程序说明。-PWM control of LED lights gradually becoming bright out procedures, has a detailed descr iption of the procedures.

海量数据题目：给定a、b两个文件，各存放50亿个url，每个url各占64字节，内存限制是4G，找出a、b文件共同的url（附生成A、B文件的程序）-Massive data problem: given a, B two files, each holding 5000000000 URL, each URL each accounted for 64 bytes, the memory limit is 4G, a, B file