Реализация суммы Минковского

vector<Vector> prepare(vector<Vector> a) {
  int n = (int)a.size();
  int i = 0;
  for (int j = 1; j < n; ++j) {
    if (make_pair(a[j].y, -a[j].x) > make_pair(a[i].y, -a[i].x)) {
      i = j;
    }
  }
  rotate(a.begin(), a.begin() + i, a.end());
  a.push_back(a[0]);
  a.push_back(a[1]);
  return a;
}

double angle(Vector a) {
  if (a.y == 0 && a.x == 0) {
    assert(false);
  }
  double ans = atan2l(a.y, a.x);
  return ans;
}

vector<Vector> sum(vector<Vector> a, vector<Vector> b) {
  int n = (int)a.size(), m = (int)b.size();
  assert(n && m);
  a = prepare(a);
  b = prepare(b);

  vector<Vector> answer;
  while (i < n || j < m) {
    answer.push_back(a[i] + b[j]);
    if (i >= n) {
      ++j;
      continue;
    }
    if (j >= m) {
      ++i;
      continue;
    }
    if (angle(vec(a[i], a[i + 1])) < angle(vec(b[j], b[j + 1]))) {
      ++i;
    } else if (angle(vec(a[i], a[i + 1])) > angle(vec(b[j], b[j + 1]))) {
      ++j;
    } else {
      assert(i < n && j < m);
      ++i;
      ++j;
    }
  }
  return answer;