Count of primes

0 <= n <= 10^3

Single input parameter n in function.

Return the count of prime numbers less than or equal to n.

Input 1:
19

Input 2:
1

Output 1:
8

Output 2:
0

Explanation 1:
Primes <= 19 are 2, 3, 5, 7, 11, 13, 17, 19

Explanation 2:
There are no primes <= 1 

public class CountPrimes {
    public int countPrimes(int n) {
        if (n <= 2) {
            return 0;
        }
 
        boolean[] isPrime = new boolean[n];
        int count = 0;
 
        for (int i = 2; i < n; i++) {
            if (!isPrime[i]) {
                count++;
                for (int j = 2; (long)i * j < n; j++) {
                    isPrime[i * j] = true;
                }
            }
        }
        return count;
    }
 
    public static void main(String[] args) {
        CountPrimes countPrimes = new CountPrimes();
        System.out.println(countPrimes.countPrimes(19)); // Output: 8
        System.out.println(countPrimes.countPrimes(1));  // Output: 0
    }
}

class Solution:
    def countPrimes(self, n: int) -> int:
        if n <= 2:
            return 0
 
        is_prime = [True] * n
        is_prime[0] = is_prime[1] = False
        count = 0
 
        for i in range(2, int(n**0.5) + 1):
            if is_prime[i]:
                is_prime[i * i: n: i] = [False] * len(is_prime[i * i: n: i])
 
        return sum(is_prime)
        
sol = Solution()
print(sol.countPrimes(19))  # Output: 8
print(sol.countPrimes(1))   # Output: 0

function countPrimes(n) {
    if (n <= 2) {
        return 0;
    }
 
    const isPrime = new Array(n).fill(true);
    isPrime[0] = isPrime[1] = false;
    let count = 0;
 
    for (let i = 2; i * i < n; i++) {
        if (isPrime[i]) {
            for (let j = i * i; j < n; j += i) {
                isPrime[j] = false;
            }
        }
    }
 
    for (let i = 2; i < n; i++) {
        if (isPrime[i]) {
            count++;
        }
    }
 
    return count;
}
 
console.log(countPrimes(19));  // Output: 8
console.log(countPrimes(1));   // Output: 0