Problem p01547 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cfloat>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <utility>
#include <vector>
using namespace std;

#define EPS 1e-7

typedef complex<double> P;
typedef const P &rP;
typedef vector<P> vP;
typedef vector<int> vint;

struct segment {
  P a, b;
  segment() {}
  segment(rP a, rP b) : a(a), b(b) {}
};

struct coninfo {
  int bnum, pnum;
  double arg;

  coninfo(int p) : pnum(p), bnum(-1), arg(0.0) {}

  bool operator<(const coninfo &c) const { return arg < c.arg; }
};

inline bool eq(double a, double b) { return abs(a - b) < EPS; }

namespace std {
bool operator<(rP a, rP b) {
  if (!eq(real(a), real(b))) {
    return real(a) < real(b);
  }
  if (!eq(imag(a), imag(b))) {
    return imag(a) < imag(b);
  }
  return false;
}
} // namespace std

double dot(rP va, rP vb) { return real(va) * real(vb) + imag(va) * imag(vb); }

double cross(rP va, rP vb) { return real(va) * imag(vb) - imag(va) * real(vb); }

int ccw(rP a, P b, P c) {
  b -= a;
  c -= a;
  if (cross(b, c) > 0)
    return +1; // counter clockwise
  if (cross(b, c) < 0)
    return -1; // clockwise
  if (dot(b, c) < 0)
    return +2; // c--a--b on line
  if (norm(b) < norm(c))
    return -2; // a--b--c on line
  return 0;
}

P intrSS(const segment &s, const segment &t) {
  P dSab = s.b - s.a;
  P dTba = t.a - t.b;
  P dSTa = t.a - s.a;

  double D = cross(dSab, dTba);

  if (abs(D) > EPS) {
    double p = cross(dSTa, dTba) / D;
    double q = cross(dSab, dSTa) / D;

    if (-EPS < p && p < 1.0 + EPS && -EPS < q && q < 1.0 + EPS) {
      return s.a + p * dSab;
    }
  }
  return P(DBL_MAX, DBL_MAX);
}

bool intersectSP(const segment &s, rP p) {
  return eq(abs(s.a - p) + abs(s.b - p), abs(s.a - s.b));
}

bool merge_if_able(segment &s, const segment &t) {
  if (abs(cross(s.b - s.a, t.b - t.a)) > EPS)
    return false;

  if (ccw(s.a, t.a, s.b) == +1 || ccw(s.a, t.a, s.b) == -1)
    return false; // not on the same line

  if (ccw(s.a, s.b, t.a) == -2 || ccw(t.a, t.b, s.a) == -2)
    return false; // separated

  s = segment(min(s.a, t.a), max(s.b, t.b));
  return true;
}

void merge_segments(vector<segment> &segs) {
  for (int i = 0; i < segs.size(); ++i)
    if (segs[i].b < segs[i].a)
      swap(segs[i].b, segs[i].a);

  for (int i = 0; i < segs.size();) {
    int inc = 1;
    for (int j = i + 1; j < segs.size(); ++j) {
      if (merge_if_able(segs[i], segs[j])) {
        segs[j--] = segs.back();
        segs.pop_back();
        inc = 0;
      }
    }

    i += inc;
  }
}

void segarrange(const vector<segment> &ss, vector<P> &ps,
                vector<vector<coninfo>> &ret) {
  for (int i = 0; i < ss.size(); ++i) { // O(n^2)
    ps.push_back(ss[i].a);
    ps.push_back(ss[i].b);
    for (int j = i + 1; j < ss.size(); ++j) {
      P intr = intrSS(ss[i], ss[j]);
      if (real(intr) < DBL_MAX) {
        ps.push_back(intr);
      }
    }
  }

  sort(ps.begin(), ps.end());
  ps.erase(unique(ps.begin(), ps.end()), ps.end());

  vector<vector<coninfo>> g(ps.size());
  for (int i = 0; i < ss.size(); ++i) {
    vector<pair<double, int>> list;
    for (int j = 0; j < ps.size(); ++j)
      if (intersectSP(ss[i], ps[j]))
        list.push_back(make_pair(norm(ss[i].a - ps[j]), j));

    sort(list.begin(), list.end());

    for (int j = 0; j + 1 < list.size(); ++j) {
      int a = list[j].second, b = list[j + 1].second;
      g[a].push_back(coninfo(b));
      g[b].push_back(coninfo(a));
    }
  }

  g.swap(ret);
}

double distance_ls_p(rP a, rP b, rP c) {
  if (dot(b - a, c - a) <= 0.0)
    return abs(c - a);
  if (dot(a - b, c - b) <= 0.0)
    return abs(c - b);
  return abs(cross(b - a, c - a)) / abs(b - a);
}

bool contains(const vector<P> &plg, rP pt) {
  int cnt = 0;
  double y = imag(pt);

  for (int i = 0; i + 1 < plg.size(); ++i) {
    int j = i + 1;

    if (distance_ls_p(plg[i], plg[j], pt) < EPS) {
      return true;
    }

    double dyi = imag(plg[i]) - y;
    double dyj = y - imag(plg[j]);
    double tx = (dyi * real(plg[j]) + dyj * real(plg[i])) / (dyi + dyj);

    if (imag(plg[i]) >= y && imag(plg[j]) < y) {
      if (tx < real(pt))
        ++cnt;
    } else if (imag(plg[i]) < y && imag(plg[j]) >= y) {
      if (tx < real(pt))
        ++cnt;
    }
  }

  return (cnt % 2 != 0);
}

P inner(const vector<P> &plg) {
  int n = plg.size() - 1;

  for (int i = 0;; ++i) {
    int j = (i + 1) % n;
    int k = (i + 2) % n;

    P cen = (plg[i] + plg[j] + plg[k]) / 3.0;
    if (contains(plg, cen))
      return cen;
  }
}

vector<vector<P>> plgs;
vector<P> pnts;
vector<vector<P>> blocks;
vector<vector<coninfo>> cons;
vector<vint> WF;
int out;

void prepare() {
  vector<segment> segs;
  segs.reserve(35);
  blocks.reserve(1000);
  for (int i = 0; i < plgs.size(); ++i) {
    for (int j = 1; j < plgs[i].size(); ++j) {
      segs.push_back(segment(plgs[i][j - 1], plgs[i][j]));
    }

    if (i > 0) {
      segs.push_back(segment(plgs[i - 1][0], plgs[i][0]));
    }
  }

  merge_segments(segs);
  segarrange(segs, pnts, cons);

  for (int i = 0; i < cons.size(); ++i) {
    for (int j = 0; j < cons[i].size(); ++j) {
      cons[i][j].arg = arg(pnts[cons[i][j].pnum] - pnts[i]);
    }
    sort(cons[i].begin(), cons[i].end());
  }

  for (int i = 0; i < cons.size(); ++i) {
    for (int j = 0; j < cons[i].size(); ++j) {
      if (cons[i][j].bnum != -1)
        continue;

      int p = i, idx = j;
      vector<P> blk;
      while (1) {
        blk.push_back(pnts[p]);
        int nxtp = cons[p][idx].pnum;
        int nxti;
        for (nxti = 0; cons[nxtp][nxti].pnum != p; ++nxti)
          ;

        --nxti;
        if (nxti < 0)
          nxti += cons[nxtp].size();

        if (cons[nxtp][nxti].bnum != -1) {
          break;
        }

        cons[nxtp][nxti].bnum = blocks.size();
        p = nxtp;
        idx = nxti;
      }

      double S = 0.0;
      for (int k = 1; k < blk.size(); ++k) {
        S += cross(blk[k - 1], blk[k]);
      }
      if (S < -EPS) {
        out = blocks.size();
      }

      blocks.push_back(blk);
    }
  }

  vint gas(blocks.size());
  for (int i = 0; i < blocks.size(); ++i) {
    if (i == out)
      continue;

    P cen = inner(blocks[i]);
    for (int j = 0; j < plgs.size(); ++j) {
      if (contains(plgs[j], cen)) {
        ++gas[i];
      }
    }
  }

  WF.assign(blocks.size(), vint(blocks.size(), 1000000000));
  for (int i = 0; i < blocks.size(); ++i) {
    WF[i][i] = 0;
  }
  for (int i = 0; i < cons.size(); ++i) {
    int k = cons[i].size() - 1;
    for (int j = 0; j < cons[i].size(); ++j) {
      int a = cons[i][k].bnum, b = cons[i][j].bnum;
      WF[a][b] = WF[b][a] = abs(gas[b] - gas[a]);
      k = j;
    }
  }

  for (int k = 0; k < blocks.size(); ++k)
    for (int i = 0; i < blocks.size(); ++i)
      for (int j = 0; j < i; ++j) {
        WF[i][j] = WF[j][i] = min(WF[i][j], WF[i][k] + WF[k][j]);
      }
}

int blocknumber(rP p) {
  for (int i = 0; i < blocks.size(); ++i) {
    if (i != out && contains(blocks[i], p)) {
      return i;
    }
  }
  return out;
}

int query(P pfrom, P pto) {
  int from = blocknumber(pfrom), to = blocknumber(pto);
  return WF[from][to];
}

int main() {
  int n, m, q, x, y, x2, y2;
  scanf("%d", &n);

  plgs.resize(n);
  for (int i = 0; i < n; ++i) {
    scanf("%d", &m);
    plgs[i].resize(m + 1);
    for (int j = 0; j < m; ++j) {
      scanf("%d%d", &x, &y);
      plgs[i][j] = P(x, y);
    }
    plgs[i][m] = plgs[i][0];
  }

  prepare();

  scanf("%d", &q);
  for (int i = 0; i < q; ++i) {
    scanf("%d%d%d%d", &x, &y, &x2, &y2);
    printf("%d\n", query(P(x, y), P(x2, y2)));
  }
}

Fixed submission:
#include <algorithm>
#include <cfloat>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <utility>
#include <vector>
using namespace std;

#define EPS 1e-9

typedef complex<double> P;
typedef const P &rP;
typedef vector<P> vP;
typedef vector<int> vint;

struct segment {
  P a, b;
  segment() {}
  segment(rP a, rP b) : a(a), b(b) {}
};

struct coninfo {
  int bnum, pnum;
  double arg;

  coninfo(int p) : pnum(p), bnum(-1), arg(0.0) {}

  bool operator<(const coninfo &c) const { return arg < c.arg; }
};

inline bool eq(double a, double b) { return abs(a - b) < EPS; }

namespace std {
bool operator<(rP a, rP b) {
  if (!eq(real(a), real(b))) {
    return real(a) < real(b);
  }
  if (!eq(imag(a), imag(b))) {
    return imag(a) < imag(b);
  }
  return false;
}
} // namespace std

double dot(rP va, rP vb) { return real(va) * real(vb) + imag(va) * imag(vb); }

double cross(rP va, rP vb) { return real(va) * imag(vb) - imag(va) * real(vb); }

int ccw(rP a, P b, P c) {
  b -= a;
  c -= a;
  if (cross(b, c) > 0)
    return +1; // counter clockwise
  if (cross(b, c) < 0)
    return -1; // clockwise
  if (dot(b, c) < 0)
    return +2; // c--a--b on line
  if (norm(b) < norm(c))
    return -2; // a--b--c on line
  return 0;
}

P intrSS(const segment &s, const segment &t) {
  P dSab = s.b - s.a;
  P dTba = t.a - t.b;
  P dSTa = t.a - s.a;

  double D = cross(dSab, dTba);

  if (abs(D) > EPS) {
    double p = cross(dSTa, dTba) / D;
    double q = cross(dSab, dSTa) / D;

    if (-EPS < p && p < 1.0 + EPS && -EPS < q && q < 1.0 + EPS) {
      return s.a + p * dSab;
    }
  }
  return P(DBL_MAX, DBL_MAX);
}

bool intersectSP(const segment &s, rP p) {
  return eq(abs(s.a - p) + abs(s.b - p), abs(s.a - s.b));
}

bool merge_if_able(segment &s, const segment &t) {
  if (abs(cross(s.b - s.a, t.b - t.a)) > EPS)
    return false;

  if (ccw(s.a, t.a, s.b) == +1 || ccw(s.a, t.a, s.b) == -1)
    return false; // not on the same line

  if (ccw(s.a, s.b, t.a) == -2 || ccw(t.a, t.b, s.a) == -2)
    return false; // separated

  s = segment(min(s.a, t.a), max(s.b, t.b));
  return true;
}

void merge_segments(vector<segment> &segs) {
  for (int i = 0; i < segs.size(); ++i)
    if (segs[i].b < segs[i].a)
      swap(segs[i].b, segs[i].a);

  for (int i = 0; i < segs.size();) {
    int inc = 1;
    for (int j = i + 1; j < segs.size(); ++j) {
      if (merge_if_able(segs[i], segs[j])) {
        segs[j--] = segs.back();
        segs.pop_back();
        inc = 0;
      }
    }

    i += inc;
  }
}

void segarrange(const vector<segment> &ss, vector<P> &ps,
                vector<vector<coninfo>> &ret) {
  for (int i = 0; i < ss.size(); ++i) { // O(n^2)
    ps.push_back(ss[i].a);
    ps.push_back(ss[i].b);
    for (int j = i + 1; j < ss.size(); ++j) {
      P intr = intrSS(ss[i], ss[j]);
      if (real(intr) < DBL_MAX) {
        ps.push_back(intr);
      }
    }
  }

  sort(ps.begin(), ps.end());
  ps.erase(unique(ps.begin(), ps.end()), ps.end());

  vector<vector<coninfo>> g(ps.size());
  for (int i = 0; i < ss.size(); ++i) {
    vector<pair<double, int>> list;
    for (int j = 0; j < ps.size(); ++j)
      if (intersectSP(ss[i], ps[j]))
        list.push_back(make_pair(norm(ss[i].a - ps[j]), j));

    sort(list.begin(), list.end());

    for (int j = 0; j + 1 < list.size(); ++j) {
      int a = list[j].second, b = list[j + 1].second;
      g[a].push_back(coninfo(b));
      g[b].push_back(coninfo(a));
    }
  }

  g.swap(ret);
}

double distance_ls_p(rP a, rP b, rP c) {
  if (dot(b - a, c - a) <= 0.0)
    return abs(c - a);
  if (dot(a - b, c - b) <= 0.0)
    return abs(c - b);
  return abs(cross(b - a, c - a)) / abs(b - a);
}

bool contains(const vector<P> &plg, rP pt) {
  int cnt = 0;
  double y = imag(pt);

  for (int i = 0; i + 1 < plg.size(); ++i) {
    int j = i + 1;

    if (distance_ls_p(plg[i], plg[j], pt) < EPS) {
      return true;
    }

    double dyi = imag(plg[i]) - y;
    double dyj = y - imag(plg[j]);
    double tx = (dyi * real(plg[j]) + dyj * real(plg[i])) / (dyi + dyj);

    if (imag(plg[i]) >= y && imag(plg[j]) < y) {
      if (tx < real(pt))
        ++cnt;
    } else if (imag(plg[i]) < y && imag(plg[j]) >= y) {
      if (tx < real(pt))
        ++cnt;
    }
  }

  return (cnt % 2 != 0);
}

P inner(const vector<P> &plg) {
  int n = plg.size() - 1;

  for (int i = 0;; ++i) {
    int j = (i + 1) % n;
    int k = (i + 2) % n;

    P cen = (plg[i] + plg[j] + plg[k]) / 3.0;
    if (contains(plg, cen))
      return cen;
  }
}

vector<vector<P>> plgs;
vector<P> pnts;
vector<vector<P>> blocks;
vector<vector<coninfo>> cons;
vector<vint> WF;
int out;

void prepare() {
  vector<segment> segs;
  segs.reserve(35);
  blocks.reserve(1000);
  for (int i = 0; i < plgs.size(); ++i) {
    for (int j = 1; j < plgs[i].size(); ++j) {
      segs.push_back(segment(plgs[i][j - 1], plgs[i][j]));
    }

    if (i > 0) {
      segs.push_back(segment(plgs[i - 1][0], plgs[i][0]));
    }
  }

  merge_segments(segs);
  segarrange(segs, pnts, cons);

  for (int i = 0; i < cons.size(); ++i) {
    for (int j = 0; j < cons[i].size(); ++j) {
      cons[i][j].arg = arg(pnts[cons[i][j].pnum] - pnts[i]);
    }
    sort(cons[i].begin(), cons[i].end());
  }

  for (int i = 0; i < cons.size(); ++i) {
    for (int j = 0; j < cons[i].size(); ++j) {
      if (cons[i][j].bnum != -1)
        continue;

      int p = i, idx = j;
      vector<P> blk;
      while (1) {
        blk.push_back(pnts[p]);
        int nxtp = cons[p][idx].pnum;
        int nxti;
        for (nxti = 0; cons[nxtp][nxti].pnum != p; ++nxti)
          ;

        --nxti;
        if (nxti < 0)
          nxti += cons[nxtp].size();

        if (cons[nxtp][nxti].bnum != -1) {
          break;
        }

        cons[nxtp][nxti].bnum = blocks.size();
        p = nxtp;
        idx = nxti;
      }

      double S = 0.0;
      for (int k = 1; k < blk.size(); ++k) {
        S += cross(blk[k - 1], blk[k]);
      }
      if (S < -EPS) {
        out = blocks.size();
      }

      blocks.push_back(blk);
    }
  }

  vint gas(blocks.size());
  for (int i = 0; i < blocks.size(); ++i) {
    if (i == out)
      continue;

    P cen = inner(blocks[i]);
    for (int j = 0; j < plgs.size(); ++j) {
      if (contains(plgs[j], cen)) {
        ++gas[i];
      }
    }
  }

  WF.assign(blocks.size(), vint(blocks.size(), 1000000000));
  for (int i = 0; i < blocks.size(); ++i) {
    WF[i][i] = 0;
  }
  for (int i = 0; i < cons.size(); ++i) {
    int k = cons[i].size() - 1;
    for (int j = 0; j < cons[i].size(); ++j) {
      int a = cons[i][k].bnum, b = cons[i][j].bnum;
      WF[a][b] = WF[b][a] = abs(gas[b] - gas[a]);
      k = j;
    }
  }

  for (int k = 0; k < blocks.size(); ++k)
    for (int i = 0; i < blocks.size(); ++i)
      for (int j = 0; j < i; ++j) {
        WF[i][j] = WF[j][i] = min(WF[i][j], WF[i][k] + WF[k][j]);
      }
}

int blocknumber(rP p) {
  for (int i = 0; i < blocks.size(); ++i) {
    if (i != out && contains(blocks[i], p)) {
      return i;
    }
  }
  return out;
}

int query(P pfrom, P pto) {
  int from = blocknumber(pfrom), to = blocknumber(pto);
  return WF[from][to];
}

int main() {
  int n, m, q, x, y, x2, y2;
  scanf("%d", &n);

  plgs.resize(n);
  for (int i = 0; i < n; ++i) {
    scanf("%d", &m);
    plgs[i].resize(m + 1);
    for (int j = 0; j < m; ++j) {
      scanf("%d%d", &x, &y);
      plgs[i][j] = P(x, y);
    }
    plgs[i][m] = plgs[i][0];
  }

  prepare();

  scanf("%d", &q);
  for (int i = 0; i < q; ++i) {
    scanf("%d%d%d%d", &x, &y, &x2, &y2);
    printf("%d\n", query(P(x, y), P(x2, y2)));
  }
}