challenge-198/deadmarshal/d/ch2.d


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import std.stdio:writeln;

bool is_prime(int n)
{
  int i = 5;
  if((n == 2) || (n == 3)) return true;
  if((n <= 1) || (n % 2 == 0) || (n % 3 == 0)) return false;
  while(i * i <= n)
  {
    if((n % i == 0) || (n % (i+2) == 0)) return false;
    i += 6;
  }
  return true;
}

int prime_count(int n)
{
  int count = 0;
  for(int i = 1; i < n-1; ++i) if(is_prime(i)) count++;
  return count;
}

void main()
{
  writeln(prime_count(10));
  writeln(prime_count(15));
  writeln(prime_count(1));
  writeln(prime_count(25));
}