求1到1000能同时被3 5 7整除的数的个数
Use inclusion/exclusion principle to calculate how many numbers between 1 and 1000 are divisible by any of 3,5,7
可能是要求用交集并集来求(设A为能被3整除的数,B为能被5整除的数,C为能被7整除的数）