[LeetCode]204. Count Primes

Description:

Count the number of prime numbers less than a non-negative number, n.

public class Solution {
    public int countPrimes(int n) {
        int res=0;
        boolean[] prime = new boolean[n]; //false:prime; true:prime
        for(int i=2; i<n; i++){
            if(!prime[i]){
                res++;
                for(int j=2;j*i<n; j++)
                    prime[j*i]=true;
            }
        }
        return res;
    }
}