I - How many prime numbers HDU - 2138

Posted 2020-10-30 神韵袖藏

 Give you a lot of positive integers, just to find out how many prime numbers there are.

Input  There are a lot of cases. In each case, there is an integer N representing the number of integers to find. Each integer won’t exceed 32-bit signed integer, and each of them won’t be less than 2.Output  For each case, print the number of prime numbers you have found out.Sample Input

3
2 3 4

Sample Output

2

最开始用打表筛选素数，居然超时间。然后猜想到这个测试的数据的数目可能不大，然后就改为检测每一个数是不是素数的方法，就ac了
#include<iostream>
#include<cmath>
using namespace std;
bool fun(int num);
int main()
{
	int datanum, num,ans;
	while (cin >> datanum)
	{
		ans = 0;
		while (datanum--)
		{
			cin >> num;
			if (num == 1) continue;
			if (num == 2 || fun(num)) ans++;
		}
		cout << ans << endl;
	}
}
bool fun(int num)
{
	for (int i = 2; i <= sqrt(num); i++)
	{
		if (num%i == 0) return false;
	}
	return true;
}