[leetcode]204. Count Primes

题目链接:https://leetcode.com/problems/count-primes/

Description:

Count the number of prime numbers less than a non-negative number, n.

class Solution{public:    vector<int> prim_vec;    bool isPrime(int n)    {        if(n<2)            return false;        if(n==2)            return true;        if(n%2==0)            return false;        int sq=int(sqrt(n));        int len=(int)prim_vec.size();        for(int i=0;i<len;i++)        {            if(prim_vec[i]>sq)                return true;            if(n%prim_vec[i]==0)                return false;        }        return true;    }    int countPrimes(int n)    {        int num=0;        for(int i=2;i<n;i++)        {            if(isPrime(i))                prim_vec.push_back(i);        }        return num;    }};