204. Count Primes

//https://leetcode.com/problems/count-primes/
class Solution {
public:
    int countPrimes(int n) {
      //  vector<int> primes(n);
        vector<bool> isp(n,true);
      //  iota(primes.begin(),primes.end(),1);
        
        
        for(int i = 2; i*i<n ; i++){
            if(!isp[i]) continue;
            for(int j = i*i ; j< n; j+=i){
                isp[j]= false;
            }
        }
        
        
    int count = 0;
   for (int i = 2; i < n; i++) {
      if (isp[i]) count++;
   }
   return count;
    }
};