소수 찾기

https://www.acmicpc.net/problem/1978

1978번: 소수 찾기

// 코드

import java.util.*;
import java.io.*;
 
public class Main{
  public static void main(String[] args) throws Exception {
 
    // Please Enter Your Code Here
    BufferedWriter bw  = new BufferedWriter(new OutputStreamWriter(System.out));
    BufferedReader br  = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = null;
    int n = Integer.parseInt(br.readLine());
    
    int max = 1000;
    boolean[] isPrime = new boolean[max+1];
    for(int i=0; i<=max; i++) {
      isPrime[i] = true;
    }
    
    for(int i=2; i<=max; i++) {
      for(int j = i*2; j<=max; j+=i) {
        if(!isPrime[j]) continue;
        isPrime[j] = false;
      }
    }
    
    int cnt = 0;
    st = new StringTokenizer(br.readLine());
    for(int i=0; i<n; i++) {
      int num = Integer.parseInt(st.nextToken());
      if(num == 1) continue;
      if(isPrime[num]) cnt++;
    }
    
    bw.write(String.valueOf(cnt));
    br.close();
    bw.flush();
    bw.close();
    
  }
}