leetcode 204. Count Primes

/***leetcode 204. Count Primes**Description:Count the number of prime numbers less than a non-negative number, n.题目大意：求小于n个素数的个数解题思路：打表，素数筛选法求素数，然后统计。*/#include <iostream>#include <string>#include <vector>#include <algorithm>using namespace std;class Solution {public:    int countPrimes(int n)     {        //打表        vector<int> isPrime(n, true);        for (int i = 2; i * i <= n; ++i)        {            if (isPrime[i])            {                //2...i，把这些数的倍数不是素数                for (int j = i *i; j < n; j += i)                    isPrime[j] = false;            }        }        int ret = 0;        for (int i = 2; i < n; ++i)            if (isPrime[i])                ++ret;        return ret;    }};void test(){    Solution sol;    cout << sol.countPrimes(10) << endl;}int main(){    test();    return 0;}