Count Primes

 1 import java.util.BitSet;
 2 
 3 public class Solution {
 4     public static int countPrimes(int n) {
 5         BitSet bs = new BitSet(n);
 6         bs.set(0); bs.set(1);
 7         int ind = 0, count = 0;
 8         while(ind < n){
 9             ind = bs.nextClearBit(ind + 1);
10             if(ind >= n)
11                 return count;
12             count++;
13             for(long i = (long)ind* (long)ind; i < n; i += ind)
14                 bs.set((int)i);
15         }
16         return count;
17     }
18 
19     public static void main(String[]args){
20     
21     System.out.println(countPrimes(1500000));
22     }
23 }