Problem p02764 (C++)

Buggy submission (status: Time Limit Exceeded):
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &o) {
  out << "(" << o.first << "," << o.second << ")";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &V) {
  for (int i = 0; i < V.size(); i++) {
    out << V[i];
    if (i != V.size() - 1)
      out << " ";
  }
  return out;
}
template <class T>
ostream &operator<<(ostream &out, const vector<vector<T>> &Mat) {
  for (int i = 0; i < Mat.size(); i++) {
    if (i != 0)
      out << endl;
    out << Mat[i];
  }
  return out;
}
template <class S, class T>
ostream &operator<<(ostream &out, const map<S, T> &mp) {
  out << "{ ";
  for (auto it = mp.begin(); it != mp.end(); it++) {
    out << it->first << ":" << it->second;
    if (mp.size() - 1 != distance(mp.begin(), it))
      out << ", ";
  }
  out << " }";
  return out;
}
template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}
template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}
template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}
/*
 <url:>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-9, pi = acos(-1.0);
namespace std {
bool operator<(const Point &lhs, const Point &rhs) {
  if (lhs.real() < rhs.real() - eps)
    return true;
  if (lhs.real() > rhs.real() + eps)
    return false;
  return lhs.imag() < rhs.imag();
}
} // namespace std
Point input_point() {
  ld x, y;
  cin >> x >> y;
  return Point(x, y);
} // 点の入力
bool eq(ld a, ld b) { return (abs(a - b) < eps); } // 誤差つき等号判定
ld dot(Point a, Point b) { return real(conj(a) * b); }   // 内積
ld cross(Point a, Point b) { return imag(conj(a) * b); } // 外積

// 直線の定義
class Line {
public:
  Point a, b;
  Line() : a(Point(0, 0)), b(Point(0, 0)) {}
  Line(Point a, Point b) : a(a), b(b) {}
  Point operator[](const int _num) {
    if (_num == 0)
      return a;
    else if (_num == 1)
      return b;
    else
      assert(false);
  }
};

// 円の定義
class Circle {
public:
  Point p;
  ld r;
  Circle() : p(Point(0, 0)), r(0) {}
  Circle(Point p, ld r) : p(p), r(r) {}
};

// 垂線の足
Point proj(Line l, Point p) {
  ld t = dot(p - l.a, l.a - l.b) / norm(l.a - l.b);
  return l.a + t * (l.a - l.b);
}

// CCW
int ccw(Point a, Point b, Point c) {
  b -= a;
  c -= a;
  if (cross(b, c) > eps)
    return 1; // a,b,cが反時計周りの順に並ぶ
  if (cross(b, c) < -eps)
    return -1; // a,b,cが時計周りの順に並ぶ
  if (dot(b, c) < 0)
    return 2; // c,a,bの順に直線に並ぶ
  if (norm(b) < norm(c))
    return -2; // a,b,cの順に直線に並ぶ
  return 0;    // a,c,bの順に直線に並ぶ
}

/* 交差判定 */
// 直線と直線の交差判定
bool isis_ll(Line l, Line m) { return !eq(cross(l.b - l.a, m.b - m.a), 0); }
// 直線と線分の交差判定
bool isis_ls(Line l, Line s) {
  return isis_ll(l, s) &&
         (cross(l.b - l.a, s.a - l.a) * cross(l.b - l.a, s.b - l.a) < eps);
}
// 線分と線分の交差判定
bool isis_ss(Line s, Line t) {
  return ccw(s.a, s.b, t.a) * ccw(s.a, s.b, t.b) <= 0 &&
         ccw(t.a, t.b, s.a) * ccw(t.a, t.b, s.b) <= 0;
}
// 点の直線上判定
bool isis_lp(Line l, Point p) { return (abs(cross(l.b - p, l.a - p)) < eps); }
// 点の線分上判定
bool isis_sp(Line s, Point p) {
  return (abs(s.a - p) + abs(s.b - p) - abs(s.b - s.a) < eps);
}

/* 距離 */
// 直線と直線の交点
Point is_ll(Line s, Line t) {
  Point sv = s.b - s.a, tv = t.b - t.a;
  assert(cross(sv, tv) != 0);
  return s.a + sv * cross(tv, t.a - s.a) / cross(tv, sv);
}

// 直線と点の距離
ld dist_lp(Line l, Point p) { return abs(p - proj(l, p)); }

// 直線と直線の距離
ld dist_ll(Line l, Line m) { return isis_ll(l, m) ? 0 : dist_lp(l, m.a); }

// 直線と線分の距離
ld dist_ls(Line l, Line s) {
  return isis_ls(l, s) ? 0 : min(dist_lp(l, s.a), dist_lp(l, s.b));
}

// 線分と点の距離
ld dist_sp(Line s, Point p) {
  Point r = proj(s, p);
  return isis_sp(s, r) ? abs(r - p) : min(abs(s.a - p), abs(s.b - p));
}

// 線分と線分の距離
ld dist_ss(Line s, Line t) {
  if (isis_ss(s, t))
    return 0;
  return min(
      {dist_sp(s, t.a), dist_sp(s, t.b), dist_sp(t, s.a), dist_sp(t, s.b)});
}

/* 円 */
// 円と円の交点
vector<Point> is_cc(Circle c1, Circle c2) {
  vector<Point> res;
  ld d = abs(c1.p - c2.p);
  ld rc = (d * d + c1.r * c1.r - c2.r * c2.r) / (2 * d);
  ld dfr = c1.r * c1.r - rc * rc;
  if (abs(dfr) < eps)
    dfr = 0.0;
  else if (dfr < 0.0)
    return res; // no intersection
  ld rs = sqrt(dfr);
  Point diff = (c2.p - c1.p) / d;
  res.push_back(c1.p + diff * Point(rc, rs));
  if (dfr != 0.0)
    res.push_back(c1.p + diff * Point(rc, -rs));
  return res;
}
// 円と直線の交点
vector<Point> is_lc(Circle c, Line l) {
  vector<Point> res;
  ld d = dist_lp(l, c.p);
  if (d < c.r + eps) {
    ld len = (d > c.r) ? 0.0 : sqrt(c.r * c.r - d * d); // safety;
    Point nor = (l.a - l.b) / abs(l.a - l.b);
    res.push_back(proj(l, c.p) + len * nor);
    res.push_back(proj(l, c.p) - len * nor);
  }
  return res;
}
// 円と線分の距離
vector<Point> is_sc(Circle c, Line l) {
  vector<Point> v = is_lc(c, l), res;
  for (Point p : v)
    if (isis_sp(l, p))
      res.push_back(p);
  return res;
}
// 円と点の接線
vector<Line> tangent_cp(Circle c, Point p) {
  vector<Line> ret;
  Point v = c.p - p;
  ld d = abs(v);
  ld l = sqrt(norm(v) - c.r * c.r);
  if (isnan(l)) {
    return ret;
  }
  Point v1 = v * Point(l / d, c.r / d);
  Point v2 = v * Point(l / d, -c.r / d);
  ret.push_back(Line(p, p + v1));
  if (l < eps)
    return ret;
  ret.push_back(Line(p, p + v2));
  return ret;
}
// 円と円の接線
vector<Line> tangent_cc(Circle c1, Circle c2) {
  vector<Line> ret;
  if (abs(c1.p - c2.p) - (c1.r + c2.r) > -eps) {
    Point center = (c1.p * c2.r + c2.p * c1.r) / (c1.r + c2.r);
    ret = tangent_cp(c1, center);
  }
  if (abs(c1.r - c2.r) > eps) {
    Point out = (-c1.p * c2.r + c2.p * c1.r) / (c1.r - c2.r);
    vector<Line> nret = tangent_cp(c1, out);
    ret.insert(ret.end(), nret.begin(), nret.end());
  } else {
    Point v = c2.p - c1.p;
    v /= abs(v);
    Point q1 = c1.p + v * Point(0, 1) * c1.r;
    Point q2 = c1.p + v * Point(0, -1) * c1.r;
    ret.push_back(Line(q1, q1 + v));
    ret.push_back(Line(q2, q2 + v));
  }
  return ret;
}

template <class Type> Type solve(Type res = Type()) {
  int N, K;
  cin >> N >> K;

  vector<int> x(N), y(N), c(N);
  for (int i = 0; i < N; i++) {
    cin >> x[i] >> y[i] >> c[i];
  }

  auto check = [&](double m) {
    vector<Circle> Cs(N);
    for (int i = 0; i < N; i++) {
      Cs[i].p = Point(x[i], y[i]);
      Cs[i].r = m / c[i];
    }
    vector<Point> cands;

    for (int i = 0; i < N; i++) {
      cands.emplace_back(Cs[i].p);
      for (int j = i + 1; j < N; j++) {
        for (const Point &p : is_cc(Cs[i], Cs[j])) {
          cands.emplace_back(p);
        }
      }
    }

    bool ok = false;

    for (const Point &p : cands) {
      int cnt = 0;
      for (int i = 0; i < N; i++) {
        if (abs(Cs[i].p - p) < Cs[i].r + eps) {
          cnt++;
        }
      }
      if (cnt >= K) {
        ok = true;
        break;
      }
    }

    return ok;
  };

  double l = 0, r = INF;
  for (int unchi = 0; unchi < 1000; unchi++) {
    double m = (l + r) / 2;

    if (check(m)) {
      r = m;
    } else {
      l = m;
    }
  }
  res = r;
  return res;
}
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  // solve<ll>(0);
  cout << fixed << setprecision(12) << solve<double>() << endl;
  return 0;
}

Fixed submission:
#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &o) {
  out << "(" << o.first << "," << o.second << ")";
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &V) {
  for (int i = 0; i < V.size(); i++) {
    out << V[i];
    if (i != V.size() - 1)
      out << " ";
  }
  return out;
}
template <class T>
ostream &operator<<(ostream &out, const vector<vector<T>> &Mat) {
  for (int i = 0; i < Mat.size(); i++) {
    if (i != 0)
      out << endl;
    out << Mat[i];
  }
  return out;
}
template <class S, class T>
ostream &operator<<(ostream &out, const map<S, T> &mp) {
  out << "{ ";
  for (auto it = mp.begin(); it != mp.end(); it++) {
    out << it->first << ":" << it->second;
    if (mp.size() - 1 != distance(mp.begin(), it))
      out << ", ";
  }
  out << " }";
  return out;
}
template <typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}
template <typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type fill_v(T &t, const V &v) {
  t = v;
}
template <typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type fill_v(T &t, const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}
/*
 <url:>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

typedef long double ld;
typedef complex<ld> Point;
const ld eps = 1e-9, pi = acos(-1.0);
namespace std {
bool operator<(const Point &lhs, const Point &rhs) {
  if (lhs.real() < rhs.real() - eps)
    return true;
  if (lhs.real() > rhs.real() + eps)
    return false;
  return lhs.imag() < rhs.imag();
}
} // namespace std
Point input_point() {
  ld x, y;
  cin >> x >> y;
  return Point(x, y);
} // 点の入力
bool eq(ld a, ld b) { return (abs(a - b) < eps); } // 誤差つき等号判定
ld dot(Point a, Point b) { return real(conj(a) * b); }   // 内積
ld cross(Point a, Point b) { return imag(conj(a) * b); } // 外積

// 直線の定義
class Line {
public:
  Point a, b;
  Line() : a(Point(0, 0)), b(Point(0, 0)) {}
  Line(Point a, Point b) : a(a), b(b) {}
  Point operator[](const int _num) {
    if (_num == 0)
      return a;
    else if (_num == 1)
      return b;
    else
      assert(false);
  }
};

// 円の定義
class Circle {
public:
  Point p;
  ld r;
  Circle() : p(Point(0, 0)), r(0) {}
  Circle(Point p, ld r) : p(p), r(r) {}
};

// 垂線の足
Point proj(Line l, Point p) {
  ld t = dot(p - l.a, l.a - l.b) / norm(l.a - l.b);
  return l.a + t * (l.a - l.b);
}

// CCW
int ccw(Point a, Point b, Point c) {
  b -= a;
  c -= a;
  if (cross(b, c) > eps)
    return 1; // a,b,cが反時計周りの順に並ぶ
  if (cross(b, c) < -eps)
    return -1; // a,b,cが時計周りの順に並ぶ
  if (dot(b, c) < 0)
    return 2; // c,a,bの順に直線に並ぶ
  if (norm(b) < norm(c))
    return -2; // a,b,cの順に直線に並ぶ
  return 0;    // a,c,bの順に直線に並ぶ
}

/* 交差判定 */
// 直線と直線の交差判定
bool isis_ll(Line l, Line m) { return !eq(cross(l.b - l.a, m.b - m.a), 0); }
// 直線と線分の交差判定
bool isis_ls(Line l, Line s) {
  return isis_ll(l, s) &&
         (cross(l.b - l.a, s.a - l.a) * cross(l.b - l.a, s.b - l.a) < eps);
}
// 線分と線分の交差判定
bool isis_ss(Line s, Line t) {
  return ccw(s.a, s.b, t.a) * ccw(s.a, s.b, t.b) <= 0 &&
         ccw(t.a, t.b, s.a) * ccw(t.a, t.b, s.b) <= 0;
}
// 点の直線上判定
bool isis_lp(Line l, Point p) { return (abs(cross(l.b - p, l.a - p)) < eps); }
// 点の線分上判定
bool isis_sp(Line s, Point p) {
  return (abs(s.a - p) + abs(s.b - p) - abs(s.b - s.a) < eps);
}

/* 距離 */
// 直線と直線の交点
Point is_ll(Line s, Line t) {
  Point sv = s.b - s.a, tv = t.b - t.a;
  assert(cross(sv, tv) != 0);
  return s.a + sv * cross(tv, t.a - s.a) / cross(tv, sv);
}

// 直線と点の距離
ld dist_lp(Line l, Point p) { return abs(p - proj(l, p)); }

// 直線と直線の距離
ld dist_ll(Line l, Line m) { return isis_ll(l, m) ? 0 : dist_lp(l, m.a); }

// 直線と線分の距離
ld dist_ls(Line l, Line s) {
  return isis_ls(l, s) ? 0 : min(dist_lp(l, s.a), dist_lp(l, s.b));
}

// 線分と点の距離
ld dist_sp(Line s, Point p) {
  Point r = proj(s, p);
  return isis_sp(s, r) ? abs(r - p) : min(abs(s.a - p), abs(s.b - p));
}

// 線分と線分の距離
ld dist_ss(Line s, Line t) {
  if (isis_ss(s, t))
    return 0;
  return min(
      {dist_sp(s, t.a), dist_sp(s, t.b), dist_sp(t, s.a), dist_sp(t, s.b)});
}

/* 円 */
// 円と円の交点
vector<Point> is_cc(Circle c1, Circle c2) {
  vector<Point> res;
  ld d = abs(c1.p - c2.p);
  ld rc = (d * d + c1.r * c1.r - c2.r * c2.r) / (2 * d);
  ld dfr = c1.r * c1.r - rc * rc;
  if (abs(dfr) < eps)
    dfr = 0.0;
  else if (dfr < 0.0)
    return res; // no intersection
  ld rs = sqrt(dfr);
  Point diff = (c2.p - c1.p) / d;
  res.push_back(c1.p + diff * Point(rc, rs));
  if (dfr != 0.0)
    res.push_back(c1.p + diff * Point(rc, -rs));
  return res;
}
// 円と直線の交点
vector<Point> is_lc(Circle c, Line l) {
  vector<Point> res;
  ld d = dist_lp(l, c.p);
  if (d < c.r + eps) {
    ld len = (d > c.r) ? 0.0 : sqrt(c.r * c.r - d * d); // safety;
    Point nor = (l.a - l.b) / abs(l.a - l.b);
    res.push_back(proj(l, c.p) + len * nor);
    res.push_back(proj(l, c.p) - len * nor);
  }
  return res;
}
// 円と線分の距離
vector<Point> is_sc(Circle c, Line l) {
  vector<Point> v = is_lc(c, l), res;
  for (Point p : v)
    if (isis_sp(l, p))
      res.push_back(p);
  return res;
}
// 円と点の接線
vector<Line> tangent_cp(Circle c, Point p) {
  vector<Line> ret;
  Point v = c.p - p;
  ld d = abs(v);
  ld l = sqrt(norm(v) - c.r * c.r);
  if (isnan(l)) {
    return ret;
  }
  Point v1 = v * Point(l / d, c.r / d);
  Point v2 = v * Point(l / d, -c.r / d);
  ret.push_back(Line(p, p + v1));
  if (l < eps)
    return ret;
  ret.push_back(Line(p, p + v2));
  return ret;
}
// 円と円の接線
vector<Line> tangent_cc(Circle c1, Circle c2) {
  vector<Line> ret;
  if (abs(c1.p - c2.p) - (c1.r + c2.r) > -eps) {
    Point center = (c1.p * c2.r + c2.p * c1.r) / (c1.r + c2.r);
    ret = tangent_cp(c1, center);
  }
  if (abs(c1.r - c2.r) > eps) {
    Point out = (-c1.p * c2.r + c2.p * c1.r) / (c1.r - c2.r);
    vector<Line> nret = tangent_cp(c1, out);
    ret.insert(ret.end(), nret.begin(), nret.end());
  } else {
    Point v = c2.p - c1.p;
    v /= abs(v);
    Point q1 = c1.p + v * Point(0, 1) * c1.r;
    Point q2 = c1.p + v * Point(0, -1) * c1.r;
    ret.push_back(Line(q1, q1 + v));
    ret.push_back(Line(q2, q2 + v));
  }
  return ret;
}

template <class Type> Type solve(Type res = Type()) {
  int N, K;
  cin >> N >> K;

  vector<int> x(N), y(N), c(N);
  for (int i = 0; i < N; i++) {
    cin >> x[i] >> y[i] >> c[i];
  }

  auto check = [&](double m) {
    vector<Circle> Cs(N);
    for (int i = 0; i < N; i++) {
      Cs[i].p = Point(x[i], y[i]);
      Cs[i].r = m / c[i];
    }
    vector<Point> cands;

    for (int i = 0; i < N; i++) {
      cands.emplace_back(Cs[i].p);
      for (int j = i + 1; j < N; j++) {
        for (const Point &p : is_cc(Cs[i], Cs[j])) {
          cands.emplace_back(p);
        }
      }
    }

    bool ok = false;

    for (const Point &p : cands) {
      int cnt = 0;
      for (int i = 0; i < N; i++) {
        if (abs(Cs[i].p - p) < Cs[i].r + eps) {
          cnt++;
        }
      }
      if (cnt >= K) {
        ok = true;
        break;
      }
    }

    return ok;
  };

  double l = 0, r = INF;
  for (int unchi = 0; unchi < 300; unchi++) {
    double m = (l + r) / 2;

    if (check(m)) {
      r = m;
    } else {
      l = m;
    }
  }
  res = r;
  return res;
}
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  // solve<ll>(0);
  cout << fixed << setprecision(12) << solve<double>() << endl;
  return 0;
}