static int vectorLength(int x, int y) {
  ret isqrt(sqr((long) x)+sqr((long) y));
}

static double vectorLength(double[] v) {
  if (l(v) == 0) ret 0;
  double sum = 0;
  for i over v:
    sum += sqr(v[i]);
  ret nthRoot(v.length, sum);
}