leetcode-python-计数质数

1）逐个判断，太慢了！

2）埃氏筛法，从2开始，1不是质数

class Solution:
    def countPrimes(self, n: int) -> int:
        isNumPrimes = [True] * n 
        count = 0  
        for i in range(2, n):
            if isNumPrimes[i]:
                count += 1
                # 使用埃拉托斯特尼 筛选法进行过滤 将合数去除
                for j in range(i*i, n, i): 
                    isNumPrimes[j] = False 
        return count