Problem p00888 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>

#define REP(i, s, n) for (int i = s; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define EPS (1e-9)
#define COUNTER_CLOCKWISE 1
#define CLOCKWISE -1
#define ONLINE_BACK 2
#define ONLINE_FRONT -2
#define ON_SEGMENT 0
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;

const int IINF = INT_MAX;

// ----------------------

class Point {
public:
  double x, y;

  Point(double x = -IINF, double y = -IINF) : 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 a) { return Point(a * x, a * y); }
  Point operator/(double a) { return Point(x / a, y / a); }
  Point operator*(Point a) {
    return Point(x * a.x - y * a.y, x * a.y + y * a.x);
  }

  bool operator<(const Point &p) const {
    return !equals(x, p.x) ? x < p.x : y < p.y;
  }

  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};

struct Segment {
  Point p1, p2;
  Segment(Point p1 = Point(), Point p2 = Point()) : p1(p1), p2(p2) {}
  bool operator==(const Segment &p) const { return p.p1 == p1 && p.p2 == p2; }
};

typedef Point Vector;
typedef Segment Line;
typedef vector<Point> Polygon;

ostream &operator<<(ostream &os, const Point &a) {
  os << "(" << a.x << "," << a.y << ")";
}

ostream &operator<<(ostream &os, const Segment &a) {
  os << "( " << a.p1 << " , " << a.p2 << " )";
}

double dot(Point a, Point b) { return a.x * b.x + a.y * b.y; }

double cross(Point a, Point b) { return a.x * b.y - a.y * b.x; }

double norm(Point a) { return a.x * a.x + a.y * a.y; }

double abs(Point a) { return sqrt(norm(a)); }

// rad は角度をラジアンで持たせること
Point rotate(Point a, double rad) {
  return Point(cos(rad) * a.x - sin(rad) * a.y,
               sin(rad) * a.x + cos(rad) * a.y);
}

// 度をラジアンに変換
double toRad(double agl) { return agl * M_PI / 180.0; }

// a => prev, b => cur, c=> next
// prev から cur へ行って next へ行く際の角度を求める
double getArg(Point a, Point b, Point c) {
  double arg1 = atan2(b.y - a.y, b.x - a.x);
  double arg2 = atan2(c.y - b.y, c.x - b.x);
  double arg = fabs(arg1 - arg2);
  while (arg > M_PI)
    arg -= 2.0 * M_PI;
  return fabs(arg);
}

int ccw(Point p0, Point p1, Point p2) {
  Point a = p1 - p0;
  Point 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 (norm(a) < norm(b))
    return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersectLL(Line l, Line m) {
  return abs(cross(l.p2 - l.p1, m.p2 - m.p1)) > EPS || // non-parallel
         abs(cross(l.p2 - l.p1, m.p1 - l.p1)) < EPS;   // same line
}
bool intersectLS(Line l, Line s) {
  return cross(l.p2 - l.p1, s.p1 - l.p1) * // s[0] is left of l
             cross(l.p2 - l.p1, s.p2 - l.p1) <
         EPS; // s[1] is right of l
}
bool intersectLP(Line l, Point p) {
  return abs(cross(l.p2 - p, l.p1 - p)) < EPS;
}
bool intersectSS(Line s, Line t) {
  return ccw(s.p1, s.p2, t.p1) * ccw(s.p1, s.p2, t.p2) <= 0 &&
         ccw(t.p1, t.p2, s.p1) * ccw(t.p1, t.p2, s.p2) <= 0;
}
bool intersectSP(Line s, Point p) {
  return abs(s.p1 - p) + abs(s.p2 - p) - abs(s.p2 - s.p1) <
         EPS; // triangle inequality
}

Point projection(Line l, Point p) {
  double t = dot(p - l.p1, l.p1 - l.p2) / norm(l.p1 - l.p2);
  return l.p1 + (l.p1 - l.p2) * t;
}
Point reflection(Line l, Point p) { return p + (projection(l, p) - p) * 2; }
double distanceLP(Line l, Point p) { return abs(p - projection(l, p)); }
double distanceLL(Line l, Line m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m.p1);
}

double distanceLS(Line l, Line s) {
  if (intersectLS(l, s))
    return 0;
  return min(distanceLP(l, s.p1), distanceLP(l, s.p2));
}
double distanceSP(Line s, Point p) {
  Point r = projection(s, p);
  if (intersectSP(s, r))
    return abs(r - p);
  return min(abs(s.p1 - p), abs(s.p2 - p));
}

double distanceSS(Line s, Line t) {
  if (intersectSS(s, t))
    return 0;
  return min(min(distanceSP(s, t.p1), distanceSP(s, t.p2)),
             min(distanceSP(t, s.p1), distanceSP(t, s.p2)));
}

Point crosspoint(Line l, Line m) {
  double A = cross(l.p2 - l.p1, m.p2 - m.p1);
  double B = cross(l.p2 - l.p1, l.p2 - m.p1);
  if (abs(A) < EPS && abs(B) < EPS) {
    vector<Point> vec;
    vec.push_back(l.p1), vec.push_back(l.p2), vec.push_back(m.p1),
        vec.push_back(m.p2);
    sort(vec.begin(), vec.end());
    assert(vec[1] == vec[2]);
    return vec[1];
    // return m.p1;
  }
  if (abs(A) < EPS)
    assert(false);
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

/*
Point crosspoint(Line l, Line m) {
  double A = cross(l.p2 - l.p1, m.p2 - m.p1);
  double B = cross(l.p2 - l.p1, l.p2 - m.p1);
  if (abs(A) < EPS && abs(B) < EPS) return m.p1; // same line
  if (abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m.p1 +   (m.p2 - m.p1) * (B / A);
}
*/

// -------------------

struct Data {
  int L, R;
  double cost;
  bool operator<(const Data &data) const { return cost > data.cost; }
};

typedef pair<int, int> ii;
int N;
Point ps[101];
// double mindist[MAX_V][MAX_V];
map<ii, double> mindist;

bool LT(double a, double b) { return !equals(a, b) && a < b; }
bool LTE(double a, double b) { return equals(a, b) || a < b; }
double getDist(double x, double y) { return sqrt(x * x + y * y); }

int getDir(Point s, Point t) {
  if (equals(s.y, t.y))
    return 0;
  if (LT(s.y, t.y))
    return 1;
  return -1;
}

// メモ化可能
ii canMove(int s, int coef, int t, const vector<Point> &vec) {
  int next_s = s + coef;
  if (!(0 <= next_s && next_s < vec.size()))
    return ii(-1, -1);
  int dir = getDir(vec[s], vec[next_s]);
  if (dir == 0)
    return ii(t, -1);

  ii ret = ii(-1, -1);
  for (int d = -1; d <= 1; d += 2) {
    int cur_t = t;
    int next_t = t + d;
    while ((0 <= next_t && next_t < vec.size()) &&
           getDir(vec[cur_t], vec[next_t]) == dir) {
      if (equals(vec[next_t].y, vec[next_s].y)) {
        if (d == -1)
          ret.first = next_t;
        else
          ret.second = next_t;
        break;
      }
      cur_t = next_t;
      next_t = next_t + d;
    }
  }
  return ret;
}

inline void compute() {
  mindist.clear();
  vector<Point> vec;
  rep(i, N) {
    vec.push_back(ps[i]);
    Segment ver = Segment(Point(-2000, ps[i].y), Point(2000, ps[i].y));
    rep(j, N - 1) {
      Segment seg = Segment(ps[j], ps[j + 1]);
      if (!equals(seg.p1.y, seg.p2.y)) {
        if (LT(min(seg.p1.y, seg.p2.y), ver.p1.y) &&
            LT(ver.p1.y, max(seg.p1.y, seg.p2.y))) {
          Point cp = crosspoint(ver, seg);
          vec.push_back(cp);
        }
      }
    }
  }

  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());

  /*
  rep(i,vec.size()) {
    cout << i << "-th : " << vec[i] << endl;
  } cout << endl;
  */
  int V = vec.size();
  // cout << "V = " << V << endl;
  priority_queue<Data> Q;
  Q.push((Data){0, V - 1, 0});
  mindist[ii(0, V - 1)] = 0;
  while (!Q.empty()) {
    Data data = Q.top();
    Q.pop();
    // cout << data.L << "," << data.R << " " << setprecision(10) << data.cost
    // << endl;
    if (data.L == data.R) {
      printf("%.10lf\\n", data.cost);
      return;
    }

    ii next;
    for (int d = -1; d <= 1; d += 2) {
      next = ii(-1, -1);
      if ((next = canMove(data.L, d * 1, data.R, vec)) != ii(-1, -1)) {
        vector<int> to;
        if (next.first != -1)
          to.push_back(next.first);
        if (next.second != -1)
          to.push_back(next.second);
        rep(j, to.size()) {
          int ext = to[j];
          double dist =
              getDist(vec[data.L].x - vec[data.L + d * 1].x,
                      vec[data.L].y - vec[data.L + d * 1].y) +
              getDist(vec[data.R].x - vec[ext].x, vec[data.R].y - vec[ext].y);
          ii p = ii(data.L + d * 1, ext);
          // cout << "(" << data.L << "," << data.R << ") to " << data.L+d*1 <<
          // "," << ext << "? ";
          if (!mindist.count(p) ||
              (mindist.count(p) && LT(data.cost + dist, mindist[p]))) {
            // cout << "YES" << endl;
            mindist[p] = data.cost + dist;
            Q.push((Data){data.L + d * 1, ext, mindist[p]});
          } // else cout << "NO" << endl;
        }
      }
    }

    for (int d = -1; d <= 1; d += 2) {
      next = ii(-1, -1);
      if ((next = canMove(data.R, d * 1, data.L, vec)) != ii(-1, -1)) {
        vector<int> to;
        if (next.first != -1)
          to.push_back(next.first);
        if (next.second != -1)
          to.push_back(next.second);
        rep(j, to.size()) {
          int ext = to[j];
          double dist =
              getDist(vec[data.R].x - vec[data.R + d * 1].x,
                      vec[data.R].y - vec[data.R + d * 1].y) +
              getDist(vec[data.L].x - vec[ext].x, vec[data.L].y - vec[ext].y);
          ii p = ii(ext, data.R + d * 1);
          // cout << "(" << data.L << "," << data.R << ") to " << ext << "," <<
          // data.R+d*1 << "? ";
          if (!mindist.count(p) ||
              (mindist.count(p) && LT(data.cost + dist, mindist[p]))) {
            // cout << "YES" << endl;
            mindist[p] = data.cost + dist;
            Q.push((Data){ext, data.R + d * 1, mindist[p]});
          } // else cout << "NO" << endl;
        }
      }
    }
  }
  assert(false);
}

int main() {
  while (cin >> N, N) {
    rep(i, N) cin >> ps[i].x >> ps[i].y;
    compute();
  }
  return 0;
}

Error: WA

Fixed submission:

#include <bits/stdc++.h>

#define REP(i, s, n) for (int i = s; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define EPS (1e-4)
#define COUNTER_CLOCKWISE 1
#define CLOCKWISE -1
#define ONLINE_BACK 2
#define ONLINE_FRONT -2
#define ON_SEGMENT 0
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;

const int IINF = INT_MAX;

// ----------------------

class Point {
public:
  double x, y;

  Point(double x = -IINF, double y = -IINF) : 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 a) { return Point(a * x, a * y); }
  Point operator/(double a) { return Point(x / a, y / a); }
  Point operator*(Point a) {
    return Point(x * a.x - y * a.y, x * a.y + y * a.x);
  }

  bool operator<(const Point &p) const {
    return !equals(x, p.x) ? x < p.x : y < p.y;
  }

  bool operator==(const Point &p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};

struct Segment {
  Point p1, p2;
  Segment(Point p1 = Point(), Point p2 = Point()) : p1(p1), p2(p2) {}
  bool operator==(const Segment &p) const { return p.p1 == p1 && p.p2 == p2; }
};

typedef Point Vector;
typedef Segment Line;
typedef vector<Point> Polygon;

ostream &operator<<(ostream &os, const Point &a) {
  os << "(" << a.x << "," << a.y << ")";
}

ostream &operator<<(ostream &os, const Segment &a) {
  os << "( " << a.p1 << " , " << a.p2 << " )";
}

double dot(Point a, Point b) { return a.x * b.x + a.y * b.y; }

double cross(Point a, Point b) { return a.x * b.y - a.y * b.x; }

double norm(Point a) { return a.x * a.x + a.y * a.y; }

double abs(Point a) { return sqrt(norm(a)); }

// rad は角度をラジアンで持たせること
Point rotate(Point a, double rad) {
  return Point(cos(rad) * a.x - sin(rad) * a.y,
               sin(rad) * a.x + cos(rad) * a.y);
}

// 度をラジアンに変換
double toRad(double agl) { return agl * M_PI / 180.0; }

// a => prev, b => cur, c=> next
// prev から cur へ行って next へ行く際の角度を求める
double getArg(Point a, Point b, Point c) {
  double arg1 = atan2(b.y - a.y, b.x - a.x);
  double arg2 = atan2(c.y - b.y, c.x - b.x);
  double arg = fabs(arg1 - arg2);
  while (arg > M_PI)
    arg -= 2.0 * M_PI;
  return fabs(arg);
}

int ccw(Point p0, Point p1, Point p2) {
  Point a = p1 - p0;
  Point 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 (norm(a) < norm(b))
    return ONLINE_FRONT;
  return ON_SEGMENT;
}

bool intersectLL(Line l, Line m) {
  return abs(cross(l.p2 - l.p1, m.p2 - m.p1)) > EPS || // non-parallel
         abs(cross(l.p2 - l.p1, m.p1 - l.p1)) < EPS;   // same line
}
bool intersectLS(Line l, Line s) {
  return cross(l.p2 - l.p1, s.p1 - l.p1) * // s[0] is left of l
             cross(l.p2 - l.p1, s.p2 - l.p1) <
         EPS; // s[1] is right of l
}
bool intersectLP(Line l, Point p) {
  return abs(cross(l.p2 - p, l.p1 - p)) < EPS;
}
bool intersectSS(Line s, Line t) {
  return ccw(s.p1, s.p2, t.p1) * ccw(s.p1, s.p2, t.p2) <= 0 &&
         ccw(t.p1, t.p2, s.p1) * ccw(t.p1, t.p2, s.p2) <= 0;
}
bool intersectSP(Line s, Point p) {
  return abs(s.p1 - p) + abs(s.p2 - p) - abs(s.p2 - s.p1) <
         EPS; // triangle inequality
}

Point projection(Line l, Point p) {
  double t = dot(p - l.p1, l.p1 - l.p2) / norm(l.p1 - l.p2);
  return l.p1 + (l.p1 - l.p2) * t;
}
Point reflection(Line l, Point p) { return p + (projection(l, p) - p) * 2; }
double distanceLP(Line l, Point p) { return abs(p - projection(l, p)); }
double distanceLL(Line l, Line m) {
  return intersectLL(l, m) ? 0 : distanceLP(l, m.p1);
}

double distanceLS(Line l, Line s) {
  if (intersectLS(l, s))
    return 0;
  return min(distanceLP(l, s.p1), distanceLP(l, s.p2));
}
double distanceSP(Line s, Point p) {
  Point r = projection(s, p);
  if (intersectSP(s, r))
    return abs(r - p);
  return min(abs(s.p1 - p), abs(s.p2 - p));
}

double distanceSS(Line s, Line t) {
  if (intersectSS(s, t))
    return 0;
  return min(min(distanceSP(s, t.p1), distanceSP(s, t.p2)),
             min(distanceSP(t, s.p1), distanceSP(t, s.p2)));
}

Point crosspoint(Line l, Line m) {
  double A = cross(l.p2 - l.p1, m.p2 - m.p1);
  double B = cross(l.p2 - l.p1, l.p2 - m.p1);
  if (abs(A) < EPS && abs(B) < EPS) {
    vector<Point> vec;
    vec.push_back(l.p1), vec.push_back(l.p2), vec.push_back(m.p1),
        vec.push_back(m.p2);
    sort(vec.begin(), vec.end());
    assert(vec[1] == vec[2]);
    return vec[1];
    // return m.p1;
  }
  if (abs(A) < EPS)
    assert(false);
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

/*
Point crosspoint(Line l, Line m) {
  double A = cross(l.p2 - l.p1, m.p2 - m.p1);
  double B = cross(l.p2 - l.p1, l.p2 - m.p1);
  if (abs(A) < EPS && abs(B) < EPS) return m.p1; // same line
  if (abs(A) < EPS) assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m.p1 +   (m.p2 - m.p1) * (B / A);
}
*/

// -------------------

struct Data {
  int L, R;
  double cost;
  bool operator<(const Data &data) const { return cost > data.cost; }
};

typedef pair<int, int> ii;
int N;
Point ps[101];
// double mindist[MAX_V][MAX_V];
map<ii, double> mindist;

bool LT(double a, double b) { return !equals(a, b) && a < b; }
bool LTE(double a, double b) { return equals(a, b) || a < b; }
double getDist(double x, double y) { return sqrt(x * x + y * y); }

int getDir(Point s, Point t) {
  if (equals(s.y, t.y))
    return 0;
  if (LT(s.y, t.y))
    return 1;
  return -1;
}

// メモ化可能
int canMove(int s, int coef, int t, const vector<Point> &vec) {
  int next_s = s + coef;
  if (!(0 <= next_s && next_s < vec.size()))
    return -1;
  int dir = getDir(vec[s], vec[next_s]);
  if (dir == 0)
    return t;

  for (int d = -1; d <= 1; d += 2) {
    int cur_t = t;
    int next_t = t + d;
    while ((0 <= next_t && next_t < vec.size()) &&
           getDir(vec[cur_t], vec[next_t]) == dir) {
      if (equals(vec[next_t].y, vec[next_s].y))
        return next_t;
      cur_t = next_t;
      next_t = next_t + d;
    }
  }
  return -1;
}

inline void compute() {
  mindist.clear();
  vector<Point> vec;
  vec.push_back(ps[0]);
  vec.push_back(ps[N - 1]);
  REP(i, 1, N - 1) {
    vec.push_back(ps[i]);
    Segment ver = Segment(Point(-2000, ps[i].y), Point(2000, ps[i].y));
    rep(j, N - 1) {
      if (j == i - 1 || j == i)
        continue;
      Segment seg = Segment(ps[j], ps[j + 1]);
      if (!equals(seg.p1.y, seg.p2.y)) {
        if (LT(min(seg.p1.y, seg.p2.y), ver.p1.y) &&
            LT(ver.p1.y, max(seg.p1.y, seg.p2.y))) {
          Point cp = crosspoint(ver, seg);
          vec.push_back(cp);
        }
      }
    }
  }

  rep(i, N - 1) if (equals(ps[i].y, ps[i + 1].y)) {
    Point np = Point((ps[i].x + ps[i + 1].x) / 2.0, ps[i].y);
    vec.push_back(np);
  }

  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());
  /*
  rep(i,vec.size()) {
    cout << vec[i] << " ";
  } cout << endl;
  */
  int V = vec.size();
  priority_queue<Data> Q;
  Q.push((Data){0, V - 1, 0});

  while (!Q.empty()) {
    Data data = Q.top();
    Q.pop();
    // cout << data.L << "," << data.R << " " << data.cost << endl;
    if (data.L == data.R) {
      printf("%.10lf\\n", data.cost);
      return;
    }

    int next;
    for (int d = -1; d <= 1; d += 2) {
      next = -1;
      if ((next = canMove(data.L, d * 1, data.R, vec)) != -1) {
        double dist =
            getDist(vec[data.L].x - vec[data.L + d * 1].x,
                    vec[data.L].y - vec[data.L + d * 1].y) +
            getDist(vec[data.R].x - vec[next].x, vec[data.R].y - vec[next].y);
        ii p = ii(data.L + d * 1, next);
        if (!mindist.count(p) ||
            (mindist.count(p) && mindist[p] > data.cost + dist)) {
          mindist[p] = data.cost + dist;
          Q.push((Data){data.L + d * 1, next, mindist[p]});
        }
      }
    }

    for (int d = -1; d <= 1; d += 2) {
      next = -1;
      if ((next = canMove(data.R, d * 1, data.L, vec)) != -1) {
        double dist =
            getDist(vec[data.R].x - vec[data.R + d * 1].x,
                    vec[data.R].y - vec[data.R + d * 1].y) +
            getDist(vec[data.L].x - vec[next].x, vec[data.L].y - vec[next].y);
        ii p = ii(next, data.R + d * 1);
        if (!mindist.count(p) ||
            (mindist.count(p) && mindist[p] > data.cost + dist)) {
          mindist[p] = data.cost + dist;
          Q.push((Data){next, data.R + d * 1, mindist[p]});
        }
      }
    }
  }
  assert(false);
}

int main() {
  while (cin >> N, N) {
    rep(i, N) cin >> ps[i].x >> ps[i].y;
    compute();
  }
  return 0;
}