Count Primes

class Solution {
public:
    int countPrimes(int n) {
        if (n<= 2) return 0;
        int count = n/2;
        bool notPrime [n];
        // for (int i=0; i<n; i++){
        //     notPrime[i]= false;
        // }
        memset(notPrime,false,n);       
        for (int i = 3; i*i<n; i+=2){
            if(notPrime[i]) continue;
            for (int j= i*i; j<n; j+= i*2){
                if(!notPrime[j]){
                    notPrime[j]= true;
                    count--;
                }
            }
        }
       return count;
    }
};