Problem p00674 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<vd> vvd;

#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()
#define FOR(i, s, e) for (ll i = s; i < (ll)e; i++)
#define TEN(x) ((ll)1e##x)

template <typename F> ld bsearch(ld lower, ld upper, ld k, ll max_loop, F f) {
  if (upper < lower)
    swap(upper, lower);
  ld nu = upper - lower, nl = 0;
  if (k < f(0))
    swap(nl, nu); // ??????????°??????´???
  REP(_, max_loop) {
    ld mid = (nl + nu) / 2;
    (f(mid + lower) > k ? nu : nl) = mid;
  }
  return (nl + nu) / 2 + lower;
}

// ?????°
#define EPS (1e-10)

// ?????????
#define X real()
#define Y imag()
#define SZ size()
#define PB(x) push_back(x)
#define PREV(x, i) (x[(i + x.SZ - 1) % x.SZ])
#define NEXT(x, i) (x[(i + 1) % x.SZ])

// ??????????????£??????
using ld = long double;
template <class T> using CR = const T &;

// ?¬??????¢??°
int sgn(ld a, ld b = 0) {
  if (a > b + EPS)
    return 1;
  if (a < b - EPS)
    return -1;
  return 0;
}

///////////////////////

// ???
using P = complex<ld>;
using G = vector<P>; // ???????¨???????
struct L : public vector<P> {
  L(P a, P b) {
    PB(a);
    PB(b);
  }
};

// ????????¢??°
namespace std {
bool operator<(P a, P b) { return sgn(a.X, b.X) ? a.X < b.X : a.Y < b.Y; }
} // namespace std

ld dot(P a, P b) { return (conj(a) * b).X; }
ld cross(P a, P b) { return (conj(a) * b).Y; }

int ccw(P a, P b, P c) { // Verified : AOJCGL1C
  b -= a;
  c -= a;
  if (sgn(cross(b, c)))
    return sgn(cross(b, c)); // clockwise(-1) or counter clockwise(1)
  if (sgn(dot(b, c)) == -1)
    return 2; // c--a--b
  if (sgn(norm(b), norm(c)) == -1)
    return -2; // a--b--c
  return 0;    // a--c--b
}

bool iLS(CR<L> l, CR<L> s, bool strict = false) {
  int a = sgn(cross(l[1] - l[0], s[0] - l[0])) *
          sgn(cross(l[1] - l[0], s[1] - l[0]));
  return strict ? a == -1 // strict
                : a <= 0; // not strict
}
P pLL(CR<L> l, CR<L> m) {
  ld a = cross(l[1] - l[0], m[1] - m[0]);
  ld b = cross(l[1] - l[0], l[1] - m[0]);
  assert(sgn(a)); // parallel or same line
  return m[0] + b / a * (m[1] - m[0]);
}
G convex_cut(CR<G> g, CR<L> l) {
  G q;
  REP(i, g.size()) {
    if (ccw(l[0], l[1], g[i]) != -1)
      q.PB(g[i]);
    L s = {g[i], NEXT(g, i)};
    if (iLS(l, s, true))
      q.PB(pLL(l, s));
  }
  return q;
}
ld area2(CR<G> g) {
  ld s = 0;
  REP(i, g.size()) s += cross(g[i], NEXT(g, i));
  return s;
}
L half_convex(CR<G> g, P p, ld lower, ld upper, ll max_loop) {
  ld ans = bsearch(lower, upper, area2(g) / 2, max_loop, [&](ld x) {
    return area2(convex_cut(g, {p, p + polar<ld>(1, x)}));
  });

  return {p, p + polar<ld>(max_loop, ans)};
}

int main() {
#ifdef _WIN32
  ifstream cin("sample.in");
  ofstream cout("sample.out");
#endif
  cin.tie(0); // cin??¨cout?????£????????????
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(50);

  while (true) {
    int n;
    cin >> n;
    if (n == 0)
      break;
    G g(n);
    REP(i, n) {
      ld x, y;
      cin >> x >> y;
      g[i].real(x);
      g[i].imag(y);
    }
    vector<ld> angles;
    angles.push_back(0);
    angles.push_back(acos(-1));
    REP(i, n) {
      ld angle = arg(g[i]);
      if (angle < 0)
        angle += acos(-1);
      angles.push_back(angle);
    }
    sort(ALL(angles));
    REP(i, angles.size() - 1) {
      L l = half_convex(g, 0, angles[i], angles[i + 1], 1000);
      G cc = convex_cut(g, l);
      if (!sgn(area2(g) / 2, area2(cc))) {
        cout << l[1].X << " " << l[1].Y << endl;
        break;
      }
    }
  }
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef vector<vd> vvd;

#define REP(i, n) for (ll i = 0; i < (n); ++i)
#define ALL(c) (c).begin(), (c).end()
#define FOR(i, s, e) for (ll i = s; i < (ll)e; i++)
#define TEN(x) ((ll)1e##x)

template <typename F> ld bsearch(ld lower, ld upper, ld k, ll max_loop, F f) {
  if (upper < lower)
    swap(upper, lower);
  ld nu = upper - lower, nl = 0;
  if (k < f(0))
    swap(nl, nu); // ??????????°??????´???
  REP(_, max_loop) {
    ld mid = (nl + nu) / 2;
    (f(mid + lower) > k ? nu : nl) = mid;
  }
  return (nl + nu) / 2 + lower;
}

// ?????°
#define EPS (1e-10)

// ?????????
#define X real()
#define Y imag()
#define SZ size()
#define PB(x) push_back(x)
#define PREV(x, i) (x[(i + x.SZ - 1) % x.SZ])
#define NEXT(x, i) (x[(i + 1) % x.SZ])

// ??????????????£??????
using ld = long double;
template <class T> using CR = const T &;

// ?¬??????¢??°
int sgn(ld a, ld b = 0) {
  if (a > b + EPS)
    return 1;
  if (a < b - EPS)
    return -1;
  return 0;
}

///////////////////////

// ???
using P = complex<ld>;
using G = vector<P>; // ???????¨???????
struct L : public vector<P> {
  L(P a, P b) {
    PB(a);
    PB(b);
  }
};

// ????????¢??°
namespace std {
bool operator<(P a, P b) { return sgn(a.X, b.X) ? a.X < b.X : a.Y < b.Y; }
} // namespace std

ld dot(P a, P b) { return (conj(a) * b).X; }
ld cross(P a, P b) { return (conj(a) * b).Y; }

int ccw(P a, P b, P c) { // Verified : AOJCGL1C
  b -= a;
  c -= a;
  if (sgn(cross(b, c)))
    return sgn(cross(b, c)); // clockwise(-1) or counter clockwise(1)
  if (sgn(dot(b, c)) == -1)
    return 2; // c--a--b
  if (sgn(norm(b), norm(c)) == -1)
    return -2; // a--b--c
  return 0;    // a--c--b
}

bool iLS(CR<L> l, CR<L> s, bool strict = false) {
  int a = sgn(cross(l[1] - l[0], s[0] - l[0])) *
          sgn(cross(l[1] - l[0], s[1] - l[0]));
  return strict ? a == -1 // strict
                : a <= 0; // not strict
}
P pLL(CR<L> l, CR<L> m) {
  ld a = cross(l[1] - l[0], m[1] - m[0]);
  ld b = cross(l[1] - l[0], l[1] - m[0]);
  assert(sgn(a)); // parallel or same line
  return m[0] + b / a * (m[1] - m[0]);
}
G convex_cut(CR<G> g, CR<L> l) {
  G q;
  REP(i, g.size()) {
    if (ccw(l[0], l[1], g[i]) != -1)
      q.PB(g[i]);
    L s = {g[i], NEXT(g, i)};
    if (iLS(l, s, true))
      q.PB(pLL(l, s));
  }
  return q;
}
ld area2(CR<G> g) {
  ld s = 0;
  REP(i, g.size()) s += cross(g[i], NEXT(g, i));
  return s;
}
L half_convex(CR<G> g, P p, ld lower, ld upper, ll max_loop) {
  ld ans = bsearch(lower, upper, area2(g) / 2, max_loop, [&](ld x) {
    return area2(convex_cut(g, {p, p + polar<ld>(1, x)}));
  });

  return {p, p + polar<ld>(max_loop, ans)};
}

int main() {
#ifdef _WIN32
  ifstream cin("sample.in");
  ofstream cout("sample.out");
#endif
  cin.tie(0); // cin??¨cout?????£????????????
  ios_base::sync_with_stdio(false);
  cout << fixed << setprecision(50);

  while (true) {
    int n;
    cin >> n;
    if (n == 0)
      break;
    G g(n);
    REP(i, n) {
      ld x, y;
      cin >> x >> y;
      g[i].real(x);
      g[i].imag(y);
    }
    vector<ld> angles;
    angles.push_back(0);
    angles.push_back(acos(-1));
    REP(i, n) {
      ld angle = arg(g[i]);
      if (angle < 0)
        angle += acos(-1);
      angles.push_back(angle);
    }
    sort(ALL(angles));
    REP(i, angles.size() - 1) {
      L l = half_convex(g, 0, angles[i], angles[i + 1], 100);
      G cc = convex_cut(g, l);
      if (!sgn(area2(g) / 2, area2(cc))) {
        cout << l[1].X << " " << l[1].Y << endl;
        break;
      }
    }
  }
  return 0;
}