LeetCode "Count Primes"

Sieve of Eratosthenes

class Solution {
public:
    int countPrimes(int n) 
　　{
        if(n < 2) return 0;

        vector<bool> rec(n + 1, false);
        int bound = floor(sqrt(n));
        int removed = 0;
        for (int i = 2; i <= bound; i++)
        {
            if (!rec[i])
            {
                for (int j = 2*i; j < n; j += i)
                {
                    if (!rec[j])
                    {
                        rec[j] = true;
                        removed++;
                    }
                }
            }
        }
        return n - 2 - removed;
    }
};