random.h

template<typename T, typename Iterator>
T* random_choose_weighted(Iterator xs, function<int (const T&)> weight)
{
  int totalweight = 0;
  const T* result = nullptr;
  while (xs) {
    T* curr = *xs;
    int cweight = weight(*curr);
    totalweight += cweight;
    if (x_chance_in_y(cweight, totalweight)) {
      result = curr;
    }
  }
  return result;
}