How many prime numbers (java)

How many prime numbers

题目链接
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

题目分析

题目意思为给你n个数,有几个素数输出几
java快速输入输出方法链接

代码实现

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;

public class Main {
	public static boolean ss(int x) {//判断素数函数
		if (x == 2 || x == 3)
			return true;
		if (x % 2 == 0 || x % 3 == 0)//加快判断
			return false;
		for (int i = 5; i <= Math.sqrt(x); i++) {//这里是i小于等于x的平方就可以判断x是否为素数了
			if (x % i == 0)
				return false;
		}
		return true;
	}

	public static void main(String[] args) throws IOException {
		StreamTokenizer in = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
		PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
		int n, s, t;
		while (in.nextToken() != StreamTokenizer.TT_EOF) {//判断文件是否输入完毕
			n = (int) in.nval;
			s = 0;
			for (int i = 0; i < n; i++) {
				in.nextToken();
				t = (int) in.nval;
				if (ss(t))
					s++;
			}
			out.println(s);
			out.flush();
		}
	}
}

案例演示