Count Primes

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

 public int countPrimes(int n) {

     ArrayList<Integer> primes = new ArrayList<Integer>();

     if (n <= ) return Math.max(, n - );

     primes.add();
     primes.add();

     for (int i = ; i <= n; i++) {
         boolean isPrime = true;
         for (int p : primes) {
             int m = i % p;
             if (m == ) {
                 isPrime = false;
                 break;
             }
         }

         if (isPrime) {
             primes.add(i);
         }
     }

     return primes.size();
 }

 class Solution {
     public int countPrimes(int n) {
         boolean[] notPrime = new boolean[n];
         int count = ;
         for (int i = ; i < n; i++) {
             if (notPrime[i] == false) {
                 count++;
                 for (int j = ; i * j < n; j++) {
                     notPrime[i * j] = true;
                 }
             }
         }
         return count;
     }
 }