prime numbers less than a given number c++
// This Function returns a vector containing all primes less than n using seive of eratosthenes
vector<long long> primes_less_than(long long n)
{
vector<long long> ans(0);
if (n <= 2)
return ans;
map<long long, bool> is_prime;
for(long long i=0; i < n; i++)
is_prime[i] = true;
is_prime[0] = false;
is_prime[1] = false;
for (long long i = 2; i < sqrt(n); i++)
if (is_prime[i])
for (long long j = i * i; j < n; j += i)
is_prime[j] = false;
for(long long i=0; i < n; i++)
if (is_prime[i] == true)
ans.push_back(i);
return ans;
}