LeetCode (Count Primes)

Problem:

Description:

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

Solutions:

C++:

class Solution {public:    int countPrimes(int n) {        vector<bool> isPrime(n, true);        int num = 0;        for(int i = 2; i < n; i++){            if(isPrime[i]){                num++;                for(int j = 2; i*j < n; j++){                    isPrime[i*j] = false;                }            }        }        return num;    }};

Python3:

class Solution:    def countPrimes(self, n):        """        :type n: int        :rtype: int        """        isPrime = [True] * n;        num = 0;        for i in range(2, n):            if(isPrime[i]):                num += 1;                isPrime[2*i:n:i] = [False]*len(isPrime[2*i:n:i]);        return num;