Problem p02301 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef double D;     // ??§?¨?????????????double???long double?????????
typedef complex<D> P; // Point
typedef pair<P, P> L; // Line
typedef vector<P> VP;
const D EPS = 1e-9; // ?¨±??????????????????????????£????????????
#define X real()
#define Y imag()
#define LE(n, m) ((n) < (m) + EPS)
#define GE(n, m) ((n) + EPS > (m))
#define EQ(n, m) (abs((n) - (m)) < EPS)
D dot(P a, P b) { return (conj(a) * b).X; }
D cross(P a, P b) { return (conj(a) * b).Y; }
int ccw(P a, P b, P c) {
  b -= a;
  c -= a;
  if (cross(b, c) > EPS)
    return +1; // counter clockwise
  if (cross(b, c) < -EPS)
    return -1; // clockwise
  if (dot(b, c) < -EPS)
    return +2; // c--a--b on line
  if (norm(b) < norm(c))
    return -2; // a--b--c on line or a==b
  return 0;    // a--c--b on line or a==c or b==c
}
namespace std {
bool operator<(const P a, const P b) {
  return a.X != b.X ? a.X < b.X : a.Y < b.Y;
}
} // namespace std
// ???????§???¢?????´?????????????????????
pair<int, int> convexDiameter(const VP &ps) {
  int n = ps.size();
  int i = min_element(ps.begin(), ps.end()) - ps.begin();
  int j = max_element(ps.begin(), ps.end()) - ps.begin();
  int maxI, maxJ;
  D maxD = 0;
  rep(_, 2 * n) {
    if (maxD < norm(ps[i] - ps[j])) {
      maxD = norm(ps[i] - ps[j]);
      maxI = i;
      maxJ = j;
    }
    if (cross(ps[i] - ps[(i + 1) % n], ps[(j + 1) % n] - ps[j]) <= 0)
      j = (j + 1) % n;
    else
      i = (i + 1) % n;
  }
  return make_pair(maxI, maxJ);
}
double dis(P a, P b) {
  return sqrt((a.X - b.X) * (a.X - b.X) + (a.Y - b.Y) * (a.Y - b.Y));
}
int main() {
  int n;
  cin >> n;
  VP v;
  while (n--) {
    double a, b;
    cin >> a >> b;
    v.push_back(P(a, b));
  }
  pair<int, int> p = convexDiameter(v);
  int x = p.first, y = p.second;
  printf("%.10f", dis(v[x], v[y]));
}

Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define r(i, n) for (int i = 0; i < n; i++)
#define R(i, a, n) for (int i = a; i < n; i++)
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)
// CCW??¨///////////////////////////////////
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;
/////////////////////////////////////////
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 a) { return Point(a * x, a * y); }
  Point operator/(double a) { return Point(x / a, y / a); }

  bool operator<(const Point &p) const { return 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 Circle {
  Point c;
  double r;
};
typedef Point vect;
struct seg {
  Point p1, p2;
};
//????????´????????????
double norm(Point p) { return p.x * p.x + p.y * p.y; }
//??¶???????????????absolute  ?????????????????¶?????????
double abs(Point p) { return sqrt(norm(p)); }
//?????????????????????????????????
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; }
//??´?????????????????¨?????\\?????????????????????
bool C90(seg s1, seg s2) {
  return equals(dot(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
//????????????????????¨?????\\??????????????????????????????????????????
bool C0(seg s1, seg s2) {
  return equals(cross(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
//?°???± ??????????????´???????????????
Point project(seg s, Point p) {
  Point base = s.p2 - s.p1;
  double r = dot(p - s.p1, base) / norm(base);
  return s.p1 + base * r;
}
//????°??????????????????????
Point reflection(seg s, Point p) { return p + (project(s, p) - p) * 2.0; }
// 2???????????¢   ???????????????
double getDistancePP(Point a, Point b) { return abs(a - b); }
//??´??????????????¢(????°?)???????????????
double getDistanceLP(seg l, Point p) {
  return abs(cross(l.p2 - l.p1, p - l.p1) / abs(l.p2 - l.p1));
}
//?????????????????¢??????????????????
double getDistanceSP(seg s, Point p) {
  if (dot(s.p2 - s.p1, p - s.p1) < 0.0)
    return abs(p - s.p1);
  if (dot(s.p1 - s.p2, p - s.p2) < 0.0)
    return abs(p - s.p2);
  return getDistanceLP(s, p);
}
//????¨?????????????????¨??????????????????????????????????
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 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(seg s1, seg s2) { return intersect(s1.p1, s1.p2, s2.p1, s2.p2); }
// 2??????????§???¢?????\\??????????????????...????????????????????????
bool squareintersect(seg s1, seg s2) {
  if (s1.p2.x < s2.p1.x || s2.p2.x < s1.p1.x)
    return 0;
  if (s1.p2.y < s2.p1.y || s2.p2.y < s1.p1.y)
    return 0;
  return 1;
}
//??????????????¢?????????????????????????????§??¨???????????????
double getDistance(seg s1, seg s2) {
  if (intersect(s1, s2))
    return 0.0;
  return min(min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)),
             min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2)));
}
//??????????????????????????????(?´????????`)
Point getCrossPoint(seg s1, seg s2) {
  Point 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 intersectCC(Circle a, Circle b) {
  double dist = abs(a.c - b.c);
  if (dist > a.r + b.r + EPS)
    return 4;
  if (dist > a.r + b.r - EPS)
    return 3;
  if (dist > abs(a.r - b.r) + EPS)
    return 2;
  if (dist > abs(a.r - b.r) - EPS)
    return 1;
  return 0;
}
//?????¨??´???????????????2?????? (LINE)
seg getCrossPoint(Circle c, seg l) {
  // assert(intersect(cc,l));
  Point pr = project(l, c.c);
  Point e = (l.p2 - l.p1) / abs(l.p2 - l.p1);
  double base = sqrt(c.r * c.r - norm(pr - c.c));
  seg pp;
  pp.p1 = (pr + e * base);
  pp.p2 = (pr - e * base);
  return pp;
}
//?????¨??´??????Line??????????????°
int getCircleLine(Circle c, seg l) {
  seg a = getCrossPoint(c, l);
  if (isnan(a.p1.x) && isnan(a.p2.y))
    return 0;
  else if (a.p1.x == a.p2.x && a.p1.y == a.p2.y)
    return 1;
  else
    return 2;
}
//??????
Point gaishin(Point a, Point b, Point c) {
  double a1, a2, b1, b2, c1, c2;
  a1 = 2 * (b.x - a.x);
  b1 = 2 * (b.y - a.y);
  c1 = a.x * a.x - b.x * b.x + a.y * a.y - b.y * b.y;
  a2 = 2 * (c.x - a.x);
  b2 = 2 * (c.y - a.y);
  c2 = a.x * a.x - c.x * c.x + a.y * a.y - c.y * c.y;
  Point p;
  p.x = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
  p.y = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
  return p;
}
// 2??????????????????
double arg(Point p) { return atan2(p.y, p.x); }
Point polar(double a, double r) { return Point(cos(r) * a, sin(r) * a); }
seg getCrossPoints(Circle c1, Circle c2) {
  // assert(intersect(c1,c2));
  double d = abs(c1.c - c2.c);
  double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
  double t = arg(c2.c - c1.c);
  seg s;
  s.p2 = c1.c + polar(c1.r, t + a);
  s.p1 = c1.c + polar(c1.r, t - a);
  return s;
}
//???????????? ????????????->2 ??????->1  ????????\\???->0
typedef vector<Point> Polygon;
int contains(Polygon g, Point p) {
  int n = g.size();
  bool x = false;
  for (int i = 0; i < n; i++) {
    Point a = g[i] - p, b = g[(i + 1) % n] - p;
    if (abs(cross(a, b)) < EPS && dot(a, b) < EPS)
      return 1;
    if (a.y > b.y)
      swap(a, b);
    if (a.y < EPS && EPS < b.y && cross(a, b) > EPS)
      x = !x;
  }
  return x ? 2 : 0;
}
//?????¢?????¢???
double Area(Polygon p) {
  double a = 0;
  for (int i = 0; i < p.size(); i++)
    a += cross(p[i], p[(i + 1) % p.size()]);
  return a / 2;
}
bool isConvex(Polygon p) {
  for (int i = 0; i < p.size(); i++) {
    if (CCW(p[(i + 1) % p.size()], p[i % p.size()], p[(i + 2) % p.size()]) == 1)
      return false;
  }
  return true;
}
Polygon andrewScan(Polygon s) {
  Polygon l, u;
  if (s.size() < 3)
    return s;
  sort(s.begin(), s.end());
  u.push_back(s[0]);
  u.push_back(s[1]);
  l.push_back(s[s.size() - 1]);
  l.push_back(s[s.size() - 2]);
  for (int i = 2; i < s.size(); i++) {
    for (int n = u.size(); n >= 2 && CCW(u[n - 2], u[n - 1], s[i]) != -1 &&
                           CCW(u[n - 2], u[n - 1], s[i]) != ONLINE_FRONT;
         n--) {
      u.pop_back();
    }
    u.push_back(s[i]);
  }
  for (int i = s.size() - 3; i >= 0; i--) {
    for (int n = l.size(); n >= 2 && CCW(l[n - 2], l[n - 1], s[i]) != -1 &&
                           CCW(l[n - 2], l[n - 1], s[i]) != ONLINE_FRONT;
         n--) {
      l.pop_back();
    }
    l.push_back(s[i]);
  }
  reverse(l.begin(), l.end());
  for (int i = u.size() - 2; i >= 1; i--)
    l.push_back(u[i]);
  return l;
}
int main() {
  int n, c = 0;
  Polygon p, a;
  Point s;
  double d = 0;
  cin >> n;
  while (n--) {
    cin >> s.x >> s.y;
    p.push_back(s);
  }
  r(i, p.size()) for (int j = i + 1; j < p.size(); j++) d =
      max(d, getDistancePP(p[i], p[j]));
  printf("%.11f\\n", d);
}