204. Count Primes

Given an integer n, return the number of prime numbers that are strictly less than n.

Example 1:
Input: n = 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.

Example 2:
Input: n = 0
Output: 0

    def countPrimes(self, n: int) -> int:
        if n <= 2:
            return 0
        primes = [1] * n
        primes[0] = primes[1] = 0
        for i in range(2, int(n**0.5) + 1):
            if primes[i] == 1:
                primes[i*i:n:i] = [0] * len(primes[i*i:n:i])

        return sum(primes)