Problem p00441 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pair<int, int>> vii;
#define rrep(i, m, n) for (int(i) = (m); (i) < (n); (i)++)
#define erep(i, m, n) for (int(i) = (m); (i) <= (n); (i)++)
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define rrev(i, m, n) for (int(i) = (n)-1; (i) >= (m); (i)--)
#define erev(i, m, n) for (int(i) = (n); (i) >= (m); (i)--)
#define rev(i, n) for (int(i) = (n)-1; (i) >= 0; (i)--)
#define vrep(i, c)                                                             \\
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define ALL(v) (v).begin(), (v).end()
#define pb push_back
#define mp make_pair
template <class T, class S> inline bool minup(T &m, const S x) {
  return m > (T)x ? (m = (T)x, true) : false;
}
template <class T, class S> inline bool maxup(T &m, const S x) {
  return m < (T)x ? (m = (T)x, true) : false;
}

static const int INF = 1000000000;
static const ll MOD = 1000000007LL;
static const double EPS = 1E-10;

template <typename S, typename T> T add(S x, T y) {
  if (abs(x + y) < EPS * (abs(x) + abs(y)))
    return 0;
  return x + y;
}
template <typename T> inline bool semieq(T x, T y) { return abs(x - y) < EPS; }
template <typename T> inline bool semige(T x, T y) { return y - x < -EPS; }
template <typename T> inline bool semile(T x, T y) { return x - y < -EPS; }

struct Point : public complex<double> {
public:
  Point(const double x = 0.0, const double y = 0.0) {
    this->real(x);
    this->imag(y);
  }
  Point(const complex<double> w) {
    this->real(w.real());
    this->imag(w.imag());
  }
  inline double dot(Point p) { return (conj(*this) * p).real(); } // ??????
  inline double det(Point p) { return (conj(*this) * p).imag(); } // ??????
};

namespace std {
inline bool operator<(const Point &a, const Point &b) {
  return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
}
} // namespace std
typedef vector<Point> Polygon;
inline Point currPoint(vector<Point> P, int i) { return P[i]; }
inline Point nextPoint(vector<Point> P, int i) { return P[(i + 1) % P.size()]; }
inline Point diffPoint(vector<Point> P, int i) {
  return nextPoint(P, i) - currPoint(P, i);
}

int ccw(Point a, Point b, Point c) {
  b -= a;
  c -= a;
  if (b.det(c) > 0.0)
    return 1; // counter clockwise
  if (b.det(c) < 0.0)
    return -1; // clockwise
  if (b.dot(c) < 0.0)
    return 2; // c--a--b on line
  if (norm(b) < norm(c))
    return -2; // a--b--c on line
  return 0;
}

struct Circle : Point {
private:
  Point p;
  double r;

public:
  Circle(Point p, double r) : p(p), r(r) {}
  Circle(double x, double y, double r) : p(Point(x, y)), r(r) {}
  inline Point center() { return this->p; }
  inline double radius() { return this->r; }
};

int intersectionDeterminationOfCC(Circle A, Circle B) {
  double d = abs(A.center() - B.center());
  if (semile(d, A.radius() - B.radius()))
    return 1; // B in A
  if (semile(d, B.radius() - A.radius()))
    return -1; // A in B
  if (semieq(d, A.radius() - B.radius()))
    return 2; // B in A????????\\???
  if (semieq(d, B.radius() - A.radius()))
    return -2; // A in B????????\\???
  if (semige(d, A.radius() + B.radius()))
    return 3; // ???????????????
  if (semieq(d, A.radius() + B.radius()))
    return -3; // ?????\\
  return 4;  // ????????£?????????
}

// ???????????????????¨±??????????????????????????????????????¨????????????????¨???????????????????
inline vector<Point> intersectionOfCCk(Circle A, Circle B) {
  vector<Point> ret(2);
  double d = abs(add(A.center(), -B.center()));
  double rc =
      (add(add(d * d, A.radius() * A.radius()), -B.radius() * B.radius()));
  double rs = sqrt(add(A.radius() * A.radius(), -rc * rc / (4.0 * d * d)));
  Point diff = (add(B.center(), -A.center()));
  ret[0] = add(A.center(), diff * Point(rc / (2.0 * d * d), (rs / d)));
  ret[1] = add(A.center(), diff * Point(rc / (2.0 * d * d), (-rs / d)));
  return ret;
}

vector<Point> intersectionOfCC(Circle A, Circle B) {
  vector<Point> ret(2);
  double x1 = A.center().real(), y1 = A.center().imag(), r1 = A.radius();
  double x2 = B.center().real(), y2 = B.center().imag(), r2 = B.radius();
  double dx = x2 - x1;
  double dy = y2 - y1;
  double a = dx * dx + dy * dy;
  double b = ((r1 * r1 - r2 * r2) / a + 1) / 2;
  double d = r1 * r1 / a - b * b;
  double x3 = x1 + dx * b;
  double y3 = y1 + dy * b;
  double x4 = -dy * sqrt(d);
  double y4 = dx * sqrt(d);
  ret[0] = Point(x3 - x4, y3 - y4);
  ret[1] = Point(x3 + x4, y3 + y4);
  return ret;
}

int n;
double x, y;
Point P[33333];
bool maze[5010][5010];

int main() {
  while (cin >> n, n) {
    rep(i, 5010) rep(j, 5010) maze[i][j] = false;
    rep(i, n) {
      cin >> x >> y;
      maze[(int)x][(int)y] = true;
      P[i] = Point(x, y);
    }

    double res = 0.0;
    rep(i, n) rep(j, i) {
      double len = abs(P[i] - P[j]) * sqrt(2.0) / 2.0;
      vector<Point> can =
          intersectionOfCC(Circle(P[i], len), Circle(P[j], len));
      int flag = 0;
      vrep(c, can) if (!semile(c->real(), 0.0) && !semile(c->imag(), 0.0)) {
        if (!semieq(c->real(), round(c->real())))
          break;
        if (!semieq(c->imag(), round(c->imag())))
          break;
        if ((int)round(c->real()) >= 5005 || (int)round(c->imag()) >= 5005)
          break;
        if (!maze[(int)round(c->real())][(int)round(c->imag())])
          break;
        flag += 1;
      }
      if (flag == 2)
        maxup(res, len * len);
    }

    cout << (int)round(res) << endl;
  }

  return 0;
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pair<int, int>> vii;
#define rrep(i, m, n) for (int(i) = (m); (i) < (n); (i)++)
#define erep(i, m, n) for (int(i) = (m); (i) <= (n); (i)++)
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define rrev(i, m, n) for (int(i) = (n)-1; (i) >= (m); (i)--)
#define erev(i, m, n) for (int(i) = (n); (i) >= (m); (i)--)
#define rev(i, n) for (int(i) = (n)-1; (i) >= 0; (i)--)
#define vrep(i, c)                                                             \\
  for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define ALL(v) (v).begin(), (v).end()
#define pb push_back
#define mp make_pair
template <class T, class S> inline bool minup(T &m, const S x) {
  return m > (T)x ? (m = (T)x, true) : false;
}
template <class T, class S> inline bool maxup(T &m, const S x) {
  return m < (T)x ? (m = (T)x, true) : false;
}

static const int INF = 1000000000;
static const ll MOD = 1000000007LL;
static const double EPS = 1E-10;

template <typename S, typename T> T add(S x, T y) {
  if (abs(x + y) < EPS * (abs(x) + abs(y)))
    return 0;
  return x + y;
}
template <typename T> inline bool semieq(T x, T y) { return abs(x - y) < EPS; }
template <typename T> inline bool semige(T x, T y) { return y - x < -EPS; }
template <typename T> inline bool semile(T x, T y) { return x - y < -EPS; }

struct Point : public complex<double> {
public:
  Point(const double x = 0.0, const double y = 0.0) {
    this->real(x);
    this->imag(y);
  }
  Point(const complex<double> w) {
    this->real(w.real());
    this->imag(w.imag());
  }
  inline double dot(Point p) { return (conj(*this) * p).real(); } // ??????
  inline double det(Point p) { return (conj(*this) * p).imag(); } // ??????
};

namespace std {
inline bool operator<(const Point &a, const Point &b) {
  return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
}
} // namespace std
typedef vector<Point> Polygon;
inline Point currPoint(vector<Point> P, int i) { return P[i]; }
inline Point nextPoint(vector<Point> P, int i) { return P[(i + 1) % P.size()]; }
inline Point diffPoint(vector<Point> P, int i) {
  return nextPoint(P, i) - currPoint(P, i);
}

int ccw(Point a, Point b, Point c) {
  b -= a;
  c -= a;
  if (b.det(c) > 0.0)
    return 1; // counter clockwise
  if (b.det(c) < 0.0)
    return -1; // clockwise
  if (b.dot(c) < 0.0)
    return 2; // c--a--b on line
  if (norm(b) < norm(c))
    return -2; // a--b--c on line
  return 0;
}

struct Circle : Point {
private:
  Point p;
  double r;

public:
  Circle(Point p, double r) : p(p), r(r) {}
  Circle(double x, double y, double r) : p(Point(x, y)), r(r) {}
  inline Point center() { return this->p; }
  inline double radius() { return this->r; }
};

int intersectionDeterminationOfCC(Circle A, Circle B) {
  double d = abs(A.center() - B.center());
  if (semile(d, A.radius() - B.radius()))
    return 1; // B in A
  if (semile(d, B.radius() - A.radius()))
    return -1; // A in B
  if (semieq(d, A.radius() - B.radius()))
    return 2; // B in A????????\\???
  if (semieq(d, B.radius() - A.radius()))
    return -2; // A in B????????\\???
  if (semige(d, A.radius() + B.radius()))
    return 3; // ???????????????
  if (semieq(d, A.radius() + B.radius()))
    return -3; // ?????\\
  return 4;  // ????????£?????????
}

// ???????????????????¨±??????????????????????????????????????¨????????????????¨???????????????????
vector<Point> intersectionOfCC(Circle A, Circle B) {
  vector<Point> ret;
  double d = abs(add(A.center(), -B.center()));
  double rc =
      (add(add(d * d, A.radius() * A.radius()), -B.radius() * B.radius()));
  double rs = sqrt(add(A.radius() * A.radius(), -rc * rc / (4.0 * d * d)));
  Point diff = (add(B.center(), -A.center()));
  ret.pb(add(A.center(), diff * Point(rc / (2.0 * d * d), (rs / d))));
  ret.pb(add(A.center(), diff * Point(rc / (2.0 * d * d), (-rs / d))));
  return ret;
}

// ???????????????????¨±??????????????????????????????????????¨????????????????¨???????????????????
vector<Point> intersectionOfCCk(Circle A, Circle B) {
  vector<Point> ret;
  double d = abs(A.center() - B.center());
  double rc =
      (d * d + A.radius() * A.radius() - B.radius() * B.radius()) / (2.0 * d);
  double rs = sqrt(A.radius() * A.radius() - rc * rc);
  Point diff = (B.center() - A.center()) / d;
  ret.pb(A.center() + diff * Point(rc, rs));
  ret.pb(A.center() + diff * Point(rc, -rs));
  return ret;
}

int n;
double x, y;
vector<Point> P;
bool maze[5010][5010];

int main() {
  while (cin >> n, n) {
    P.clear();
    rep(i, 5010) rep(j, 5010) maze[i][j] = false;
    rep(i, n) {
      cin >> x >> y;
      maze[(int)x][(int)y] = true;
      P.pb(Point(x, y));
    }

    double res = 0.0;
    rep(i, P.size()) rep(j, i) {
      double len = abs(P[i] - P[j]) / sqrt(2.0); //* sqrt(2.0) / 2.0;
      vector<Point> can =
          intersectionOfCC(Circle(P[i], len), Circle(P[j], len));
      int flag = 0;
      vrep(c, can) if (!semile(c->real(), 0.0) && !semile(c->imag(), 0.0)) {
        if (!semieq(c->real(), round(c->real())))
          break;
        if (!semieq(c->imag(), round(c->imag())))
          break;
        if ((int)round(c->real()) >= 5005 || (int)round(c->imag()) >= 5005)
          break;
        if (!maze[(int)round(c->real())][(int)round(c->imag())])
          break;
        flag += 1;
      }
      if (flag == 2)
        maxup(res, len * len);
    }

    cout << (int)round(res) << endl;
  }

  return 0;
}