Problem p01128 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#define f first
#define s second
#define mp make_pair
#define inf 100000000
#define eps (1e-11)
#define equals(a, b) (fabs((a) - (b)) < eps)
using namespace std;

class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}

  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double k) { return Point(x * k, y * k); }
  Point operator/(double k) { return Point(x / k, y / k); }
  bool operator<(Point p) const { return (x != p.x ? x < p.x : y < p.y); }
  bool operator==(Point p) const {
    return fabs(x - p.x) < eps && fabs(y - p.y) < eps;
  }

  double abs() { return sqrt(norm()); }
  double norm() { return (x * x + y * y); }
};
typedef Point Vector;
typedef vector<Point> Polygon;

class Segment {
public:
  Point p1, p2;
  Segment(Point p1 = Point(0, 0), Point p2 = Point(0, 0)) : p1(p1), p2(p2) {}
};
typedef Segment Line;

double norm(Vector a) { return (a.x * a.x + a.y * a.y); }
double abs(Vector a) { return sqrt(norm(a)); }
double dot(Vector a, Vector b) { return (a.x * b.x + a.y * b.y); }
double cross(Vector a, Vector b) { return (a.x * b.y - a.y * b.x); }

static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

int ccw(Point p0, Point p1, Point p2) {
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if (cross(a, b) > eps)
    return COUNTER_CLOCKWISE;
  if (cross(a, b) < -eps)
    return CLOCKWISE;
  if (dot(a, b) < -eps)
    return ONLINE_BACK;
  if (a.norm() < b.norm())
    return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersect(Point p1, Point p2, Point p3, Point p4) {
  return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 &&
          ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}

bool intersect(Segment s1, Segment s2) {
  return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}

Point getCrossPointSS(Segment s1, Segment s2) {
  Vector base = s2.p2 - s2.p1;
  double d1 = abs(cross(base, s1.p1 - s2.p1));
  double d2 = abs(cross(base, s1.p2 - s2.p1));
  double t = d1 / (d1 + d2);
  return (s1.p1 + (s1.p2 - s1.p1) * t);
}

int main() {
  int n, N, a, b, c, d, e, f;
  Segment AB;
  vector<pair<Segment, pair<int, int>>> railroad;

  cin >> n;
  for (int k = 0; k < n; k++) {
    railroad.clear();
    cin >> AB.p1.x >> AB.p1.y >> AB.p2.x >> AB.p2.y;
    cin >> N;
    for (int i = 0; i < N; i++) {
      cin >> a >> b >> c >> d >> e >> f;
      railroad.push_back(mp(Segment(Point(a, b), Point(c, d)), mp(e, f)));
    }
    vector<pair<Point, pair<int, int>>> vp;
    for (int i = 0; i < N; i++) {
      if (!intersect(AB, railroad[i].f))
        continue;
      Point p = getCrossPointSS(AB, railroad[i].f);
      vp.push_back(mp(p, mp(railroad[i].s.f, railroad[i].s.s)));
    }
    sort(vp.begin(), vp.end());
    if (AB.p1 < AB.p2)
      reverse(vp.begin(), vp.end());
    int ans = 0, s;

    for (int i = 0; i < vp.size(); i++) {
      if (i == 0) {
        if (vp[i].s.f == 1)
          s = vp[0].s.s;
        if (vp[i].s.f == 0)
          s = (vp[0].s.s + 1) % 2;
      } else {
        if (vp[i].s.f == 1) {
          if (vp[i].s.s != s) {
            ans++;
            s = vp[i].s.s;
          }
        }
        if (vp[i].s.f == 0) {
          if (vp[i].s.s == s) {
            ans++;
            s = (vp[i].s.s + 1) % 2;
          }
        }
      }
    }
    cout << ans << endl;
  }
  return 0;
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
#define f first
#define s second
#define mp make_pair
#define inf 100000000
#define eps (1e-11)
#define equals(a, b) (fabs((a) - (b)) < eps)
using namespace std;

class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}

  Point operator+(Point p) { return Point(x + p.x, y + p.y); }
  Point operator-(Point p) { return Point(x - p.x, y - p.y); }
  Point operator*(double k) { return Point(x * k, y * k); }
  Point operator/(double k) { return Point(x / k, y / k); }
  bool operator<(Point p) const { return (x != p.x ? x < p.x : y < p.y); }
  bool operator==(Point p) const {
    return fabs(x - p.x) < eps && fabs(y - p.y) < eps;
  }

  double abs() { return sqrt(norm()); }
  double norm() { return (x * x + y * y); }
};
typedef Point Vector;
typedef vector<Point> Polygon;

class Segment {
public:
  Point p1, p2;
  Segment(Point p1 = Point(0, 0), Point p2 = Point(0, 0)) : p1(p1), p2(p2) {}
};
typedef Segment Line;

double norm(Vector a) { return (a.x * a.x + a.y * a.y); }
double abs(Vector a) { return sqrt(norm(a)); }
double dot(Vector a, Vector b) { return (a.x * b.x + a.y * b.y); }
double cross(Vector a, Vector b) { return (a.x * b.y - a.y * b.x); }

static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

int ccw(Point p0, Point p1, Point p2) {
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if (cross(a, b) > eps)
    return COUNTER_CLOCKWISE;
  if (cross(a, b) < -eps)
    return CLOCKWISE;
  if (dot(a, b) < -eps)
    return ONLINE_BACK;
  if (a.norm() < b.norm())
    return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersect(Point p1, Point p2, Point p3, Point p4) {
  return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 &&
          ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}

bool intersect(Segment s1, Segment s2) {
  return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}

Point getCrossPointSS(Segment s1, Segment s2) {
  Vector base = s2.p2 - s2.p1;
  double d1 = abs(cross(base, s1.p1 - s2.p1));
  double d2 = abs(cross(base, s1.p2 - s2.p1));
  double t = d1 / (d1 + d2);
  return (s1.p1 + (s1.p2 - s1.p1) * t);
}

int main() {
  int n, N, a, b, c, d, e, f;
  Segment AB;
  vector<pair<Segment, pair<int, int>>> railroad;

  cin >> n;
  for (int k = 0; k < n; k++) {
    railroad.clear();
    cin >> AB.p1.x >> AB.p1.y >> AB.p2.x >> AB.p2.y;
    cin >> N;
    for (int i = 0; i < N; i++) {
      cin >> a >> b >> c >> d >> e >> f;
      railroad.push_back(mp(Segment(Point(a, b), Point(c, d)), mp(e, f)));
    }
    vector<pair<Point, pair<int, int>>> vp;
    for (int i = 0; i < N; i++) {
      if (!intersect(AB, railroad[i].f))
        continue;
      Point p = getCrossPointSS(AB, railroad[i].f);
      vp.push_back(mp(p, mp(railroad[i].s.f, railroad[i].s.s)));
    }
    sort(vp.begin(), vp.end());
    if (AB.p1 < AB.p2)
      reverse(vp.begin(), vp.end());
    int ans = 0, s;
    if (vp[0].s.f == 1)
      s = vp[0].s.s;
    if (vp[0].s.f == 0)
      s = (vp[0].s.s + 1) % 2;
    for (int i = 1; i < vp.size(); i++) {
      if (vp[i].s.f == 1) {
        if (vp[i].s.s != s) {
          ans++;
          s = vp[i].s.s;
        }
      }
      if (vp[i].s.f == 0) {
        if (vp[i].s.s == s) {
          ans++;
          s = (vp[i].s.s + 1) % 2;
        }
      }
    }
    cout << ans << endl;
  }
  return 0;
}