Problem p00752 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <vector>

#define REP(i, s, n) for (int i = s; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define inf (1 << 29)
#define EPS (1e-5)
#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;

//

class Point {
public:
  double x, y;

  Point(double x = -inf, double y = -inf) : 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); }

  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(-inf, -inf), Point p2 = Point(-inf, -inf))
      : 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; }

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)
    return m.p1; // same line
  if (abs(A) < EPS)
    assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

//

int n;
vector<Segment> seg;
Point s, t;

double compute(double rad) {
  Point e = Point(cos(rad), sin(rad));
  e = e * 1000;
  e = e + s;
  Segment UruruBeam = Segment(s, e);

  double ret = 0;
  Point sp;
  int onSeg = -1;
  sp = s;
  rep(i, 6) {
    double mdist = inf;
    Point mcp;
    int mp = -1;
    rep(j, n) if (onSeg != j && intersectSS(UruruBeam, seg[j])) {
      Point cp = crosspoint(UruruBeam, seg[j]);
      double dist = abs(sp - cp);
      if (!equals(mdist, dist) && mdist > dist) {
        mdist = dist;
        mcp = cp;
        mp = j;
      }
    }

    if (intersectSP(UruruBeam, t)) {
      double dist = abs(sp - t);
      if (!equals(mdist, dist) && mdist > dist)
        return ret + dist;
    }

    if (mp == -1)
      return inf;

    onSeg = mp;
    ret += abs(sp - mcp);
    UruruBeam = Segment(mcp, reflection(seg[mp], UruruBeam.p2));
    sp = mcp;
  }
  return inf;
}

int main() {
  while (scanf("%d", &n), n) {
    seg.clear();
    seg.resize(n);
    rep(i, n) scanf("%lf %lf %lf %lf", &seg[i].p1.x, &seg[i].p1.y, &seg[i].p2.x,
                    &seg[i].p2.y);
    scanf("%lf %lf", &t.x, &t.y);
    scanf("%lf %lf", &s.x, &s.y);

    double ans = inf;
    for (double theta = 0.0, cnt = 0; cnt <= 3600000; theta += 0.0001, cnt++) {
      ans = min(ans, compute(toRad(theta)));
    }
    printf("%.10lf\n", ans);
  }
  return 0;
}

Fixed submission:
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <vector>

#define REP(i, s, n) for (int i = s; i < n; i++)
#define rep(i, n) REP(i, 0, n)
#define inf (1 << 29)
#define EPS (1e-5)
#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;

//

class Point {
public:
  double x, y;

  Point(double x = -inf, double y = -inf) : 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); }

  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(-inf, -inf), Point p2 = Point(-inf, -inf))
      : 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; }

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)
    return m.p1; // same line
  if (abs(A) < EPS)
    assert(false); // !!!PRECONDITION NOT SATISFIED!!!
  return m.p1 + (m.p2 - m.p1) * (B / A);
}

//

int n;
vector<Segment> seg;
Point s, t;

double compute(double rad) {
  Point e = Point(cos(rad), sin(rad));
  e = e * 1000;
  e = e + s;
  Segment UruruBeam = Segment(s, e);

  double ret = 0;
  Point sp;
  int onSeg = -1;
  sp = s;
  rep(i, 6) {
    double mdist = inf;
    Point mcp;
    int mp = -1;
    rep(j, n) if (onSeg != j && intersectSS(UruruBeam, seg[j])) {
      Point cp = crosspoint(UruruBeam, seg[j]);
      double dist = abs(sp - cp);
      if (!equals(mdist, dist) && mdist > dist) {
        mdist = dist;
        mcp = cp;
        mp = j;
      }
    }

    if (intersectSP(UruruBeam, t)) {
      double dist = abs(sp - t);
      if (!equals(mdist, dist) && mdist > dist)
        return ret + dist;
    }

    if (mp == -1)
      return inf;

    onSeg = mp;
    ret += abs(sp - mcp);
    UruruBeam = Segment(mcp, reflection(seg[mp], UruruBeam.p2));
    sp = mcp;
  }
  return inf;
}

int main() {
  while (scanf("%d", &n), n) {
    seg.clear();
    seg.resize(n);
    rep(i, n) scanf("%lf %lf %lf %lf", &seg[i].p1.x, &seg[i].p1.y, &seg[i].p2.x,
                    &seg[i].p2.y);
    scanf("%lf %lf", &t.x, &t.y);
    scanf("%lf %lf", &s.x, &s.y);

    double ans = inf;
    for (double theta = 0.0, cnt = 0; cnt <= 360000; theta += 0.001, cnt++) {
      ans = min(ans, compute(toRad(theta)));
    }
    printf("%.10lf\n", ans);
  }
  return 0;
}