leetcode 统计所有小于非负整数 n 的质数的数量

class Solution:
    def countPrimes(self, n):
        """
        :type n: int
        :rtype: int
        """
        isPrime = [1] * max(2, n)
        isPrime[0],isPrime[1]=False,False
        x = 2
        while x * x < n:
            if isPrime[x]:
                p = x * x
                while p < n:
                    isPrime[p] = 0
                    p += x
            x +=1
        return (sum(isPrime))