Problem p01252 (C++) — buggy submission, verdict: Runtime Error

/*
方針
0. 初期状態で既にAliceが見えているか判定 =(YES)=> 0.000 と出力して終わる
1. Bombと長方形の角を結ぶ線分を列挙
   線分は建物の角とぶつかるor平行であるならそのまま伸ばしていく (
建物につっこんだら終了 )
2. Aliceから各点 ( 建物の角、線分の端点 ) への最短距離を求める
3. 各点から直接到達可能なBombの線分をみつけ、その点までの距離 +
その点からBombの線分までの最短距離を計算し、最も短いものを記録
 */

#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-5)
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;

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;

bool LT(double a, double b) { return !equals(a, b) && a < b; }
bool LTE(double a, double b) { return equals(a, b) || a < b; }

class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
  Point operator+(const Point &p) { return Point(x + p.x, y + p.y); }
  Point operator-(const 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*(const 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 : (!equals(y, p.y) && 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 &s) const {
    return (p1 == s.p1) ? p2 < s.p2 : p1 < s.p1;
  }
  bool operator==(const Segment &p) const {
    return (p.p1 == p1 && p.p2 == p2) || (p.p1 == p2 && p.p2 == p1);
  }
};

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

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

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 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 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));
}

Point nearest_point(Segment seg, Point p) {
  Point r = projection(seg, p);
  if (intersectSP(seg, r))
    return r;
  if (LT(abs(seg.p1 - p), abs(seg.p2 - p)))
    return seg.p1;
  return seg.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]); // 同じセグメントかもよ
    return vec[1];
  }
  if (abs(A) < EPS)
    assert(false);
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

double cross3p(Point p, Point q, Point r) {
  return (r.x - q.x) * (p.y - q.y) - (r.y - q.y) * (p.x - q.x);
}

bool collinear(Point p, Point q, Point r) {
  return fabs(cross3p(p, q, r)) < EPS;
}

bool onSegment(Point p, Point q, Point r) {
  return collinear(p, q, r) &&
         equals(sqrt(pow(p.x - r.x, 2) + pow(p.y - r.y, 2)) +
                    sqrt(pow(r.x - q.x, 2) + pow(r.y - q.y, 2)),
                sqrt(pow(p.x - q.x, 2) + pow(p.y - q.y, 2)));
}

// 多角形poly内（線分上も含む）に点pが存在するかどうは判定する
inline bool inPolygon(Polygon poly, Point p, int on) {
  if (LT(poly[0].x, p.x) && LT(p.x, poly[3].x) && LT(poly[0].y, p.y) &&
      LT(p.y, poly[1].y))
    return true;
  return false;
}

const double DINF = 1e20;
const int MAX_N = 40;
int N;
Point ps[40][2];
Point A, B;

Point vir;
bool comp_dist(const Point &p1, const Point &p2) {
  return LT(abs(vir - p1), abs(vir - p2));
}

// target_segがtriesのいづれかと交差しているか? true -> 交差してる false ->
// してない
bool intersect_checker(const vector<Polygon> &tries, Segment target_seg) {
  rep(i, tries.size()) {
    vector<Point> vp;
    vp.push_back(target_seg.p1);
    vp.push_back(target_seg.p2);
    rep(j, tries[i].size()) {
      Segment seg = Segment(tries[i][j], tries[i][(j + 1) % tries[i].size()]);
      if (equals(cross(target_seg.p1 - target_seg.p2, seg.p1 - seg.p2), 0.0)) {
        if (onSegment(target_seg.p1, target_seg.p2, seg.p1))
          vp.push_back(seg.p1);
        if (onSegment(target_seg.p1, target_seg.p2, seg.p2))
          vp.push_back(seg.p2);
      } else {
        if (intersectSS(target_seg, seg))
          vp.push_back(crosspoint(target_seg, seg));
      }
    }
    sort(vp.begin(), vp.end());
    vp.erase(unique(vp.begin(), vp.end()), vp.end());
    vir = target_seg.p1;
    sort(vp.begin(), vp.end(), comp_dist);
    rep(k, (int)vp.size() - 1) {
      Point mp = (vp[k] + vp[k + 1]) / 2.0;
      if (inPolygon(tries[i], mp, 0))
        return true;
    }
  }
  return false;
}

inline bool containAnyPolygon(vector<Polygon> &polies, Point p) {
  rep(i, polies.size()) if (LT(polies[i][0].x, p.x) &&
                            LT(p.x, polies[i][3].x) &&
                            LT(polies[i][0].y, p.y) &&
                            LT(p.y, polies[i][1].y)) return true;
  return false;
}

vector<Segment> createBombLine(vector<Polygon> &tries, Point sp) {
  Polygon surround(4);
  surround[0] = Point(-20000, -20000);
  surround[1] = Point(-20000, 20000); // 制約のミスを知らないとここで落ちる
  surround[2] = Point(20000, 20000);
  surround[3] = Point(20000, -20000);
  vector<Segment> ret;
  rep(i, tries.size()) rep(j, tries[i].size()) {
    if (sp == tries[i][j])
      continue;
    Vector e = (tries[i][j] - sp) / abs(tries[i][j] - sp);
    Segment line = Segment(sp, sp + e * 100000);
    vector<Point> vp;
    vp.push_back(sp);
    vp.push_back(tries[i][j]);
    rep(k, 4) {
      if (equals(cross(surround[k] - surround[(k + 1) % 4], line.p1 - line.p2),
                 0.0))
        continue;
      Segment seg = Segment(surround[k], surround[(k + 1) % 4]);
      if (intersectSS(line, seg))
        vp.push_back(crosspoint(line, seg));
    }

    rep(k, tries.size()) rep(l, tries[k].size()) {
      Segment seg = Segment(tries[k][l], tries[k][(l + 1) % tries[k].size()]);
      if (equals(cross(seg.p1 - seg.p2, line.p1 - line.p2), 0.0))
        continue;
      if (intersectSS(seg, line))
        vp.push_back(crosspoint(seg, line));
    }

    sort(vp.begin(), vp.end());
    vp.erase(unique(vp.begin(), vp.end()), vp.end());
    vir = sp;
    sort(vp.begin(), vp.end(), comp_dist);
    rep(k, (int)vp.size() - 1) {
      Segment seg = Segment(vp[k], vp[k + 1]);
      Point mp = (seg.p1 + seg.p2) / 2.0;
      if (containAnyPolygon(tries, mp))
        break;
      ret.push_back(seg);
    }
  }
  sort(ret.begin(), ret.end());
  ret.erase(unique(ret.begin(), ret.end()), ret.end());
  return ret;
}

void makeGraph(const vector<Point> &vp, vector<vector<int>> &G,
               vector<Polygon> &tries) {
  int V = vp.size();
  rep(i, V) {
    REP(j, i + 1, V) {
      if (intersect_checker(tries, Segment(vp[i], vp[j])))
        continue;
      G[i].push_back(j);
      G[j].push_back(i);
    }
  }
}

// Aliceから各点への最短距離を求める
struct Data {
  int cur;
  double weight;
  bool operator<(const Data &data) const {
    return !equals(weight, data.weight) && weight > data.weight;
  }
};

void dijkstra(const vector<vector<int>> &G, vector<Point> &vp,
              vector<double> &mindist) {
  int V = vp.size();
  int sp = -1;
  rep(i, V) if (vp[i] == A) {
    sp = i;
    break;
  }
  assert(sp != -1);
  mindist[sp] = 0;
  priority_queue<Data> Q;
  Q.push((Data){sp, 0});
  while (!Q.empty()) {
    Data data = Q.top();
    Q.pop();
    if (LT(mindist[data.cur], data.weight))
      continue;
    rep(i, G[data.cur].size()) {
      int to = G[data.cur][i];
      if (LT(data.weight + abs(vp[data.cur] - vp[to]), mindist[to])) {
        mindist[to] = data.weight + abs(vp[data.cur] - vp[to]);
        Q.push((Data){to, mindist[to]});
      }
    }
  }
}

void compute() {
  vector<Polygon> tries;
  rep(i, N) {
    Polygon poly;
    poly.push_back(ps[i][0]);
    poly.push_back(Point(ps[i][0].x, ps[i][1].y));
    poly.push_back(ps[i][1]);
    poly.push_back(Point(ps[i][1].x, ps[i][0].y));
    tries.push_back(poly);
  }

  if (!intersect_checker(tries, Segment(A, B))) {
    puts("0.000");
    return;
  }

  vector<Segment> segs = createBombLine(tries, B);

  vector<Point> vp;
  vp.push_back(A);
  rep(i, tries.size()) rep(j, tries[i].size()) vp.push_back(tries[i][j]);
  rep(i, segs.size()) rep(j, tries.size()) rep(k, tries[j].size()) {
    if (equals(cross(segs[i].p1 - segs[i].p2,
                     tries[j][k] - tries[j][(k + 1) % tries[j].size()]),
               0.0))
      continue;
    Segment seg = Segment(tries[j][k], tries[j][(k + 1) % tries[j].size()]);
    if (intersectSS(segs[i], seg))
      vp.push_back(crosspoint(segs[i], seg));
  }

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

  int V = vp.size();
  vector<vector<int>> G(V, vector<int>());
  makeGraph(vp, G, tries);

  vector<double> mindist(V, DINF);
  dijkstra(G, vp, mindist);

  double answer = DINF;
  rep(i, vp.size()) {
    if (LTE(answer, mindist[i]))
      continue;
    rep(j, segs.size()) {
      double dist = mindist[i] + distanceSP(segs[j], vp[i]);
      if (LTE(answer, dist))
        continue;
      Point np = nearest_point(segs[j], vp[i]);
      Segment seg = Segment(vp[i], np);
      if (intersect_checker(tries, seg))
        continue;
      answer = dist;
    }
  }
  printf("%.6lf\\n", answer);
}

int main() {
  while (scanf("%d", &N), N) {
    rep(i, N) rep(j, 2) scanf("%lf %lf", &ps[i][j].x, &ps[i][j].y);
    scanf("%lf %lf %lf %lf", &A.x, &A.y, &B.x, &B.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-5)
#define equals(a, b) (fabs((a) - (b)) < EPS)

using namespace std;

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;

bool LT(double a, double b) { return !equals(a, b) && a < b; }
bool LTE(double a, double b) { return equals(a, b) || a < b; }

class Point {
public:
  double x, y;

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

  Point operator+(const Point &p) { return Point(x + p.x, y + p.y); }
  Point operator-(const 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*(const 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 : (!equals(y, p.y) && 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 &s) const {
    return (p1 == s.p1) ? p2 < s.p2 : p1 < s.p1;
  }
  bool operator==(const Segment &p) const {
    return (p.p1 == p1 && p.p2 == p2) || (p.p1 == p2 && p.p2 == p1);
  }
};

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(const Point &a, const Point &b) { return a.x * b.x + a.y * b.y; }

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

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

double abs(const 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 nearest_point(Segment seg, Point p) {
  Point r = projection(seg, p);
  if (intersectSP(seg, r))
    return r;
  if (LT(abs(seg.p1 - p), abs(seg.p2 - p)))
    return seg.p1;
  return seg.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]); // 同じセグメントかもよ
    return vec[1];
  }
  if (abs(A) < EPS)
    assert(false);
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

double cross3p(Point p, Point q, Point r) {
  return (r.x - q.x) * (p.y - q.y) - (r.y - q.y) * (p.x - q.x);
}

bool collinear(Point p, Point q, Point r) {
  return fabs(cross3p(p, q, r)) < EPS;
}

bool ccwtest(Point p, Point q, Point r) { return cross3p(p, q, r) > 0; }

bool onSegment(Point p, Point q, Point r) {
  return collinear(p, q, r) &&
         equals(sqrt(pow(p.x - r.x, 2) + pow(p.y - r.y, 2)) +
                    sqrt(pow(r.x - q.x, 2) + pow(r.y - q.y, 2)),
                sqrt(pow(p.x - q.x, 2) + pow(p.y - q.y, 2)));
}

double angle(Point a, Point b, Point c) {
  double ux = b.x - a.x, uy = b.y - a.y;
  double vx = c.x - a.x, vy = c.y - a.y;
  return acos((ux * vx + uy * vy) /
              sqrt((ux * ux + uy * uy) * (vx * vx + vy * vy)));
}

// 多角形poly内（線分上も含む）に点pが存在するかどうは判定する
inline bool inPolygon(Polygon poly, Point p, int on) {
  if (LT(poly[0].x, p.x) && LT(p.x, poly[3].x) && LT(poly[0].y, p.y) &&
      LT(p.y, poly[1].y))
    return true;
  return false;
  /*
  if((int)poly.size() == 0)return false;
  if( on ) rep(i,poly.size())
  if(onSegment(poly[i],poly[(i+1)%poly.size()],p))return true; double sum = 0;
  for(int i=0; i < (int)poly.size() ;i++) {
    if( equals(cross(poly[i]-p,poly[(i+1)%poly.size()]-p),0.0) ) continue;
    if(cross3p(p,poly[i],poly[(i+1)%poly.size()]) < 0)
      sum -= angle(p,poly[i],poly[(i+1)%poly.size()]);
    else
      sum += angle(p,poly[i],poly[(i+1)%poly.size()]);
  }
  const double eps = 1e-5;
  return (fabs(sum - 2*M_PI) < eps || fabs(sum + 2*M_PI) < eps);
  */
}

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

const double DINF = 1e20;
const int MAX_N = 40;
int N;
Point ps[40][2];
Point A, B;

Point vir;
bool comp_dist(const Point &p1, const Point &p2) {
  return LT(abs(vir - p1), abs(vir - p2));
}

// target_segがtriesのいづれかと交差しているか? true -> 交差してる false ->
// してない
bool intersect_checker(const vector<Polygon> &tries, Segment target_seg) {
  rep(i, tries.size()) {
    vector<Point> vp;
    vp.push_back(target_seg.p1);
    vp.push_back(target_seg.p2);
    rep(j, tries[i].size()) {
      Segment seg = Segment(tries[i][j], tries[i][(j + 1) % tries[i].size()]);
      if (equals(cross(target_seg.p1 - target_seg.p2, seg.p1 - seg.p2), 0.0)) {
        if (onSegment(target_seg.p1, target_seg.p2, seg.p1))
          vp.push_back(seg.p1);
        if (onSegment(target_seg.p1, target_seg.p2, seg.p2))
          vp.push_back(seg.p2);
      } else {
        if (intersectSS(target_seg, seg))
          vp.push_back(crosspoint(target_seg, seg));
      }
    }
    sort(vp.begin(), vp.end());
    vp.erase(unique(vp.begin(), vp.end()), vp.end());
    vir = target_seg.p1;
    sort(vp.begin(), vp.end(), comp_dist);
    rep(k, (int)vp.size() - 1) {
      Point mp = (vp[k] + vp[k + 1]) / 2.0;
      if (inPolygon(tries[i], mp, 0))
        return true;
    }
  }
  return false;
  /*
  rep(i,tries.size()){
    rep(j,tries[i].size()){
      Segment seg = Segment(tries[i][j],tries[i][(j+1)%tries[i].size()]);
      if( equals(cross(target_seg.p1-target_seg.p2,seg.p1-seg.p2),0.0) )
  continue; if( intersectSS(target_seg,seg) ) { if(
  onSegment(target_seg.p1,target_seg.p2,seg.p1) ||
  onSegment(target_seg.p1,target_seg.p2,seg.p2) ) continue; if(
  onSegment(seg.p1,seg.p2,target_seg.p1) ||
  onSegment(seg.p1,seg.p2,target_seg.p2) ) continue; return true;
      }
    }
  }
  return false;
  */
}

inline bool containAnyPolygon(vector<Polygon> &polies, Point p) {
  rep(i, polies.size()) {
    // if( inPolygon(polies[i],p,0) ) return true;
    if (LT(polies[i][0].x, p.x) && LT(p.x, polies[i][3].x) &&
        LT(polies[i][0].y, p.y) && LT(p.y, polies[i][1].y))
      return true;
  }
  return false;
}

vector<Segment> createBombLine(vector<Polygon> &tries, Point sp) {
  Polygon surround(4);
  surround[0] = Point(-20000, -20000);
  surround[1] = Point(-20000, 20000);
  surround[2] = Point(20000, 20000);
  surround[3] = Point(20000, -20000);
  vector<Segment> ret;
  rep(i, tries.size()) rep(j, tries[i].size()) {
    if (sp == tries[i][j])
      continue;
    Vector e = (tries[i][j] - sp) / abs(tries[i][j] - sp);
    Segment line = Segment(sp, sp + e * 100000);
    vector<Point> vp;
    vp.push_back(sp);
    vp.push_back(tries[i][j]);
    rep(k, 4) {
      if (equals(cross(surround[k] - surround[(k + 1) % 4], line.p1 - line.p2),
                 0.0))
        continue;
      Segment seg = Segment(surround[k], surround[(k + 1) % 4]);
      if (intersectSS(line, seg))
        vp.push_back(crosspoint(line, seg));
    }

    rep(k, tries.size()) rep(l, tries[k].size()) {
      Segment seg = Segment(tries[k][l], tries[k][(l + 1) % tries[k].size()]);
      if (equals(cross(seg.p1 - seg.p2, line.p1 - line.p2), 0.0))
        continue;
      if (intersectSS(seg, line))
        vp.push_back(crosspoint(seg, line));
    }

    sort(vp.begin(), vp.end());
    vp.erase(unique(vp.begin(), vp.end()), vp.end());
    vir = sp;
    sort(vp.begin(), vp.end(), comp_dist);
    rep(k, (int)vp.size() - 1) {
      Segment seg = Segment(vp[k], vp[k + 1]);
      Point mp = (seg.p1 + seg.p2) / 2.0;
      if (containAnyPolygon(tries, mp))
        break;
      ret.push_back(seg);
    }
  }
  sort(ret.begin(), ret.end());
  ret.erase(unique(ret.begin(), ret.end()), ret.end());
  return ret;
}

void makeGraph(const vector<Point> &vp, vector<vector<int>> &G,
               vector<Polygon> &tries) {
  int V = vp.size();
  rep(i, V) {
    REP(j, i + 1, V) {
      if (intersect_checker(tries, Segment(vp[i], vp[j])))
        continue;
      G[i].push_back(j);
      G[j].push_back(i);
    }
  }
}

// Aliceから各点への最短距離を求める
struct Data {
  int cur;
  double weight;
  bool operator<(const Data &data) const {
    return !equals(weight, data.weight) && weight > data.weight;
  }
};

void dijkstra(const vector<vector<int>> &G, vector<Point> &vp,
              vector<double> &mindist) {
  int V = vp.size();
  int sp = -1;
  rep(i, V) if (vp[i] == A) {
    sp = i;
    break;
  }
  assert(sp != -1);
  mindist[sp] = 0;
  priority_queue<Data> Q;
  Q.push((Data){sp, 0});
  while (!Q.empty()) {
    Data data = Q.top();
    Q.pop();

    if (LT(mindist[data.cur], data.weight))
      continue;

    rep(i, G[data.cur].size()) {
      int to = G[data.cur][i];
      if (LT(data.weight + abs(vp[data.cur] - vp[to]), mindist[to])) {
        mindist[to] = data.weight + abs(vp[data.cur] - vp[to]);
        Q.push((Data){to, mindist[to]});
      }
    }
  }
}

void compute() {
  vector<Polygon> tries;
  rep(i, N) {
    Polygon poly;
    poly.push_back(ps[i][0]);
    poly.push_back(Point(ps[i][0].x, ps[i][1].y));
    poly.push_back(ps[i][1]);
    poly.push_back(Point(ps[i][1].x, ps[i][0].y));
    tries.push_back(poly);
  }

  // Bomb can find Alice already
  if (!intersect_checker(tries, Segment(A, B))) {
    puts("0.000");
    return;
  }

  vector<Segment> segs = createBombLine(tries, B);

  // rep(i,(int)segs.size()) cout << segs[i] << endl;

  vector<Point> vp;
  vp.push_back(A);
  rep(i, tries.size()) rep(j, tries[i].size()) vp.push_back(tries[i][j]);
  rep(i, segs.size()) rep(j, tries.size()) rep(k, tries[j].size()) {
    if (equals(cross(segs[i].p1 - segs[i].p2,
                     tries[j][k] - tries[j][(k + 1) % tries[j].size()]),
               0.0))
      continue;
    Segment seg = Segment(tries[j][k], tries[j][(k + 1) % tries[j].size()]);
    if (intersectSS(segs[i], seg))
      vp.push_back(crosspoint(segs[i], seg));
  }

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

  int V = vp.size();
  vector<vector<int>> G(V, vector<int>());
  makeGraph(vp, G, tries);

  vector<double> mindist(V, DINF);
  dijkstra(G, vp, mindist);

  // rep(i,V) cout << vp[i] << " " << mindist[i] << endl;

  double answer = DINF;
  rep(i, vp.size()) {
    if (LTE(answer, mindist[i]))
      continue;
    rep(j, segs.size()) {
      double dist = mindist[i] + distanceSP(segs[j], vp[i]);
      if (LTE(answer, dist))
        continue;
      Point np = nearest_point(segs[j], vp[i]);
      Segment seg = Segment(vp[i], np);
      if (intersect_checker(tries, seg))
        continue;
      answer = dist;
    }
  }
  assert(!equals(answer, DINF));
  printf("%.6lf\\n", answer);
}

int main() {
  while (cin >> N, N) {
    rep(i, N) rep(j, 2) cin >> ps[i][j].x >> ps[i][j].y;
    cin >> A.x >> A.y >> B.x >> B.y;
    rep(i, N) rep(j, 2) {
      assert(-1000 <= ps[i][j].x && ps[i][j].x <= 1000);
      assert(-1000 <= ps[i][j].y && ps[i][j].y <= 1000);
    }

    assert(-1000 <= A.x && A.x <= 1000);
    assert(-1000 <= A.y && A.y <= 1000);

    assert(-1000 <= B.x && B.x <= 1000);
    assert(-1000 <= B.y && B.y <= 1000);

    compute();
  }
  return 0;
}