//TLEclass Solution {private:    bool isPrime(int n) {        if (n <= 1)            return false;        for (int i = 2; i * i <= n; i++) {            if (n % i == 0)                return false;        }        return true;    }public:    int coutPrimes(int n) {        int count = 0;        for (int i = 1; i < n; i++) {            if (isPrime(i))                count++;        }        return count;    }};//筛数法class Solution2 {public:    int countPrimes(int n) {        if (n <= 1) return 0;        bool* IsPrime = new bool[n];        for (int i = 2; i < n; i++) {            IsPrime[i] = true;        }        for (int i = 2; i * i < n; i++) {            if (!IsPrime[i])                continue;            for (int j = i * i; j < n; j += i) {                IsPrime[j] = false;            }        }        int count = 0;        for (int i = 2; i < n; i++) {            if (IsPrime[i])                count++;        }        return count;    }};