Sieve of Eratosthenes algorithm

Question

I am currently reading \"Programming: Principles and Practice Using C++\", in Chapter 4 there is an exercise in which:

I need to mak

Answer 1

below is my version which basically uses a bit vector of bool and then goes through the odd numbers and a fast add to find multiples to set to false. In the end a vector is constructed and returned to the client of the prime values.

std::vector  getSieveOfEratosthenes ( int max )
{
  std::vector primes(max, true);
  int sz = primes.size();

  for ( int i = 3; i < sz ; i+=2 )
    if ( primes[i] ) 
      for ( int j = i * i; j < sz; j+=i)
        primes[j] = false;

  std::vector ret;
  ret.reserve(primes.size());
  ret.push_back(2);

  for ( int i = 3; i < sz; i+=2 )
    if ( primes[i] )
      ret.push_back(i);

  return ret;
}