Count Primes

[code]class Solution {
public:
    int countPrimes(int n) {
        bool *arr = new bool[n + 1];

        for(int i = 2; i < n; i++)
            arr[i] = true;

        for(int i = 2; i * i < n; i++) {
            for(int j = i * i; j < n; j = j + i) {
                arr[j] = false; 
            }
        }

        int counter = 0;
        for(int i = 2; i < n; i++) {
            if(arr[i]) 
                counter++;
        }

        return counter;
    }
};