void setup() {
  println(meanAngle(350, 10));
  println(meanAngle(90, 180, 270, 360));
  println(meanAngle(10, 20, 30));
}

float meanAngle(float... angles) {
  float sum1 = 0, sum2 = 0;
  for (int i = 0; i < angles.length; i++) {
    sum1 += sin(radians(angles[i])) / angles.length;
    sum2 += cos(radians(angles[i])) / angles.length;
  }
  return degrees(atan2(sum1, sum2));
}