SRM 431 div1 (practice)

Easy – LaserShooting

Calculate expected numbers for each obstacles, and then sum up these numbers. The way to calculate the expected number for the obstacle is that (the angle of laser to hit the obstacle) / (pi). In this problem the position (x, y) of obstacle is given, so we can calculate the angle using arc tangent.

class LaserShooting {
public:
  double numberOfHits(vector <int> x, vector <int> y1, vector <int> y2) {
    double ret = 0;

    for (int i=0; i<x.size(); i++) {
      double ang1 = atan((double)y1[i] / (double)x[i]);
      double ang2 = atan((double)y2[i] / (double)x[i]);
      ret += abs(ang1 - ang2) / M_PI;
    }

    return ret;
  }
};