[백준 1978]소수 찾기 - JAVA 풀이

import java.util.*;
import java.io.*;

public class Main
{  
    public static void main(String args[]) throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        int N = Integer.parseInt(br.readLine());        
        StringTokenizer st = new StringTokenizer(br.readLine());  
        
        boolean[] c = calc();
        int result = 0;
        
        for(int i = 0; i < N; i++){
            if(!c[Integer.parseInt(st.nextToken())])
                result++;
        }
        System.out.println(result);
    }
    
    public static boolean[] calc(){
        boolean[] check = new boolean[1001];
        check[1] = true;
        
        for(int i = 2; i < 1001; i++){
            if(check[i])
                continue;
            for(int j = i*2; j < 1001; j+=i)
                check[j] = true;            
        }
        
        return check;
    }
}