598F-F-CutLength.cpp

// url:https://codeforces.com/contest/598/problem/F
// time:2023-04-23 21:58:50
// name:F-CutLength

#include <bits/stdc++.h>

using i64 = long long;
template<class T>
struct Point {
    T x;
    T y;
    Point(T x_ = 0, T y_ = 0) : x(x_), y(y_) {}
    
    template<class U>
    operator Point<U>() {
        return Point<U>(U(x), U(y));
    }
    Point &operator+=(Point p) & {
        x += p.x;
        y += p.y;
        return *this;
    }
    Point &operator-=(Point p) & {
        x -= p.x;
        y -= p.y;
        return *this;
    }
    Point &operator*=(T v) & {
        x *= v;
        y *= v;
        return *this;
    }
    Point operator-() const {
        return Point(-x, -y);
    }
    friend Point operator+(Point a, Point b) {
        return a += b;
    }
    friend Point operator-(Point a, Point b) {
        return a -= b;
    }
    friend Point operator*(Point a, T b) {
        return a *= b;
    }
    friend Point operator*(T a, Point b) {
        return b *= a;
    }
    friend bool operator==(Point a, Point b) {
        return a.x == b.x && a.y == b.y;
    }
    friend std::istream &operator>>(std::istream &is, Point &p) {
        return is >> p.x >> p.y;
    }
    friend std::ostream &operator<<(std::ostream &os, Point p) {
        return os << "(" << p.x << ", " << p.y << ")";
    }
};

template<class T>
T dot(Point<T> a, Point<T> b) {
    return a.x * b.x + a.y * b.y;
}

template<class T>
T cross(Point<T> a, Point<T> b) {
    return a.x * b.y - a.y * b.x;
}

template<class T>
T square(Point<T> p) {
    return dot(p, p);
}

template<class T>
double length(Point<T> p) {
    return std::sqrt(double(square(p)));
}

long double length(Point<long double> p) {
    return std::sqrt(square(p));
}

template<class T>
struct Line {
    Point<T> a;
    Point<T> b;
    Line(Point<T> a_ = Point<T>(), Point<T> b_ = Point<T>()) : a(a_), b(b_) {}
};

template<class T>
Point<T> rotate(Point<T> a) {
    return Point(-a.y, a.x);
}

template<class T>
int sgn(Point<T> a) {
    return a.y > 0 || (a.y == 0 && a.x > 0) ? 1 : -1;
}

template<class T>
bool pointOnLineLeft(Point<T> p, Line<T> l) {
    return cross(l.b - l.a, p - l.a) > 0;
}

template<class T>
Point<T> lineIntersection(Line<T> l1, Line<T> l2) {
    return l1.a + (l1.b - l1.a) * (cross(l2.b - l2.a, l1.a - l2.a) / cross(l2.b - l2.a, l1.a - l1.b));
}

constexpr long double eps = 1E-8;

template<class T>
bool pointOnSegment(Point<T> p, Line<T> l) {
    return std::abs(cross(p - l.a, l.b - l.a)) < eps && std::min(l.a.x, l.b.x) < p.x + eps && p.x - eps < std::max(l.a.x, l.b.x)
        && std::min(l.a.y, l.b.y) < p.y + eps && p.y - eps < std::max(l.a.y, l.b.y);
}

template<class T>
bool pointInPolygon(Point<T> a, std::vector<Point<T>> p) {
    int n = p.size();
    for (int i = 0; i < n; i++) {
        if (pointOnSegment(a, Line(p[i], p[(i + 1) % n]))) {
            return true;
        }
    }
    
    int t = 0;
    for (int i = 0; i < n; i++) {
        auto u = p[i];
        auto v = p[(i + 1) % n];
        if (u.x < a.x && v.x >= a.x && pointOnLineLeft(a, Line(v, u))) {
            t ^= 1;
        }
        if (u.x >= a.x && v.x < a.x && pointOnLineLeft(a, Line(u, v))) {
            t ^= 1;
        }
    }
    
    return t == 1;
}

// 0 : not intersect
// 1 : strictly intersect
// 2 : overlap
// 3 : intersect at endpoint
template<class T>
std::tuple<int, Point<T>, Point<T>> segmentIntersection(Line<T> l1, Line<T> l2) {
    if (std::max(l1.a.x, l1.b.x) < std::min(l2.a.x, l2.b.x)) {
        return {0, Point<T>(), Point<T>()};
    }
    if (std::min(l1.a.x, l1.b.x) > std::max(l2.a.x, l2.b.x)) {
        return {0, Point<T>(), Point<T>()};
    }
    if (std::max(l1.a.y, l1.b.y) < std::min(l2.a.y, l2.b.y)) {
        return {0, Point<T>(), Point<T>()};
    }
    if (std::min(l1.a.y, l1.b.y) > std::max(l2.a.y, l2.b.y)) {
        return {0, Point<T>(), Point<T>()};
    }
    if (cross(l1.b - l1.a, l2.b - l2.a) == 0) {
        if (cross(l1.b - l1.a, l2.a - l1.a) != 0) {
            return {0, Point<T>(), Point<T>()};
        } else {
            auto maxx1 = std::max(l1.a.x, l1.b.x);
            auto minx1 = std::min(l1.a.x, l1.b.x);
            auto maxy1 = std::max(l1.a.y, l1.b.y);
            auto miny1 = std::min(l1.a.y, l1.b.y);
            auto maxx2 = std::max(l2.a.x, l2.b.x);
            auto minx2 = std::min(l2.a.x, l2.b.x);
            auto maxy2 = std::max(l2.a.y, l2.b.y);
            auto miny2 = std::min(l2.a.y, l2.b.y);
            Point<T> p1(std::max(minx1, minx2), std::max(miny1, miny2));
            Point<T> p2(std::min(maxx1, maxx2), std::min(maxy1, maxy2));
            if (!pointOnSegment(p1, l1)) {
                std::swap(p1.y, p2.y);
            }
            if (p1 == p2) {
                return {3, p1, p2};
            } else {
                return {2, p1, p2};
            }
        }
    }
    auto cp1 = cross(l2.a - l1.a, l2.b - l1.a);
    auto cp2 = cross(l2.a - l1.b, l2.b - l1.b);
    auto cp3 = cross(l1.a - l2.a, l1.b - l2.a);
    auto cp4 = cross(l1.a - l2.b, l1.b - l2.b);
    
    if ((cp1 > 0 && cp2 > 0) || (cp1 < 0 && cp2 < 0) || (cp3 > 0 && cp4 > 0) || (cp3 < 0 && cp4 < 0)) {
        return {0, Point<T>(), Point<T>()};
    }
    
    Point p = lineIntersection(l1, l2);
    if (cp1 != 0 && cp2 != 0 && cp3 != 0 && cp4 != 0) {
        return {1, p, p};
    } else {
        return {3, p, p};
    }
}

template<class T>
bool segmentInPolygon(Line<T> l, std::vector<Point<T>> p) {
    int n = p.size();
    if (!pointInPolygon(l.a, p)) {
        return false;
    }
    if (!pointInPolygon(l.b, p)) {
        return false;
    }
    for (int i = 0; i < n; i++) {
        auto u = p[i];
        auto v = p[(i + 1) % n];
        auto w = p[(i + 2) % n];
        auto [t, p1, p2] = segmentIntersection(l, Line(u, v));
        
        if (t == 1) {
            return false;
        }
        if (t == 0) {
            continue;
        }
        if (t == 2) {
            if (pointOnSegment(v, l) && v != l.a && v != l.b) {
                if (cross(v - u, w - v) > 0) {
                    return false;
                }
            }
        } else {
            if (p1 != u && p1 != v) {
                if (pointOnLineLeft(l.a, Line(v, u))
                    || pointOnLineLeft(l.b, Line(v, u))) {
                    return false;
                }
            } else if (p1 == v) {
                if (l.a == v) {
                    if (pointOnLineLeft(u, l)) {
                        if (pointOnLineLeft(w, l)
                            && pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    } else {
                        if (pointOnLineLeft(w, l)
                            || pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    }
                } else if (l.b == v) {
                    if (pointOnLineLeft(u, Line(l.b, l.a))) {
                        if (pointOnLineLeft(w, Line(l.b, l.a))
                            && pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    } else {
                        if (pointOnLineLeft(w, Line(l.b, l.a))
                            || pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    }
                } else {
                    if (pointOnLineLeft(u, l)) {
                        if (pointOnLineLeft(w, Line(l.b, l.a))
                            || pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    } else {
                        if (pointOnLineLeft(w, l)
                            || pointOnLineLeft(w, Line(u, v))) {
                            return false;
                        }
                    }
                }
            }
        }
    }
    return true;
}

template<class T>
std::vector<Point<T>> hp(std::vector<Line<T>> lines) {
    std::sort(lines.begin(), lines.end(), [&](auto l1, auto l2) {
        auto d1 = l1.b - l1.a;
        auto d2 = l2.b - l2.a;
        
        if (sgn(d1) != sgn(d2)) {
            return sgn(d1) == 1;
        }
        
        return cross(d1, d2) > 0;
    });
    
    std::deque<Line<T>> ls;
    std::deque<Point<T>> ps;
    for (auto l : lines) {
        if (ls.empty()) {
            ls.push_back(l);
            continue;
        }
        
        while (!ps.empty() && !pointOnLineLeft(ps.back(), l)) {
            ps.pop_back();
            ls.pop_back();
        }
        
        while (!ps.empty() && !pointOnLineLeft(ps[0], l)) {
            ps.pop_front();
            ls.pop_front();
        }
        
        if (cross(l.b - l.a, ls.back().b - ls.back().a) == 0) {
            if (dot(l.b - l.a, ls.back().b - ls.back().a) > 0) {
                
                if (!pointOnLineLeft(ls.back().a, l)) {
                    assert(ls.size() == 1);
                    ls[0] = l;
                }
                continue;
            }
            return {};
        }
        
        ps.push_back(lineIntersection(ls.back(), l));
        ls.push_back(l);
    }
    
    while (!ps.empty() && !pointOnLineLeft(ps.back(), ls[0])) {
        ps.pop_back();
        ls.pop_back();
    }
    if (ls.size() <= 2) {
        return {};
    }
    ps.push_back(lineIntersection(ls[0], ls.back()));
    
    return std::vector(ps.begin(), ps.end());
}

template<class T>
struct Frac {
    T num;
    T den;
    Frac(T num_, T den_) : num(num_), den(den_) {
        if (den < 0) {
            den = -den;
            num = -num;
        }
    }
    Frac() : Frac(0, 1) {}
    Frac(T num_) : Frac(num_, 1) {}
    explicit operator double() const {
        return 1. * num / den;
    }
    Frac &operator+=(const Frac &rhs) {
        num = num * rhs.den + rhs.num * den;
        den *= rhs.den;
        return *this;
    }
    Frac &operator-=(const Frac &rhs) {
        num = num * rhs.den - rhs.num * den;
        den *= rhs.den;
        return *this;
    }
    Frac &operator*=(const Frac &rhs) {
        num *= rhs.num;
        den *= rhs.den;
        return *this;
    }
    Frac &operator/=(const Frac &rhs) {
        num *= rhs.den;
        den *= rhs.num;
        if (den < 0) {
            num = -num;
            den = -den;
        }
        return *this;
    }
    friend Frac operator+(Frac lhs, const Frac &rhs) {
        return lhs += rhs;
    }
    friend Frac operator-(Frac lhs, const Frac &rhs) {
        return lhs -= rhs;
    }
    friend Frac operator*(Frac lhs, const Frac &rhs) {
        return lhs *= rhs;
    }
    friend Frac operator/(Frac lhs, const Frac &rhs) {
        return lhs /= rhs;
    }
    friend Frac operator-(const Frac &a) {
        return Frac(-a.num, a.den);
    }
    friend bool operator==(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den == rhs.num * lhs.den;
    }
    friend bool operator!=(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den != rhs.num * lhs.den;
    }
    friend bool operator<(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den < rhs.num * lhs.den;
    }
    friend bool operator>(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den > rhs.num * lhs.den;
    }
    friend bool operator<=(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den <= rhs.num * lhs.den;
    }
    friend bool operator>=(const Frac &lhs, const Frac &rhs) {
        return lhs.num * rhs.den >= rhs.num * lhs.den;
    }
    friend std::ostream &operator<<(std::ostream &os, Frac x) {
        T g = std::gcd(x.num, x.den);
        if (x.den == g) {
            return os << x.num / g;
        } else {
            return os << x.num / g << "/" << x.den / g;
        }
    }
};

using P = Point<Frac<__int128>>;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int n, m;
    std::cin >> n >> m;
    
    std::vector<P> p(n);
    for (int i = 0; i < n; i++) {
        double x, y;
        std::cin >> x >> y;
        p[i] = {round(x * 100), round(y * 100)};
    }
    
    std::vector<P> q;
    for (auto p : p) {
        if (q.size() >= 2 && cross(p - q.back(), q.back() - q.end()[-2]) == 0) {
            q.pop_back();
        }
        q.push_back(p);
    }
    if (cross(q[0] - q[1], q.back() - q[0]) == 0) {
        q.erase(q.begin());
    }
    if (cross(q[0] - q.back(), q.back() - q.end()[-2]) == 0) {
        q.pop_back();
    }
    p = q;
    n = p.size();
    
    std::cout << std::fixed << std::setprecision(10);
    
    while (m--) {
        P a, b;
        double ax, ay, bx, by;
        std::cin >> ax >> ay >> bx >> by;
        a = {round(ax * 100), round(ay * 100)};
        b = {round(bx * 100), round(by * 100)};
        
        double ans = 0;
        
        Line l(a, b);
        std::vector<Point<double>> q, r;
        std::vector<std::pair<Point<double>, int>> e;
        for (int i = 0; i < n; i++) {
            Point c = p[i], d = p[(i+1) % n];
            
            if (cross(a - b, c - d) == 0) {
                if (cross(a - b, a - c) == 0) {
                    r.push_back(c);
                    r.push_back(d);
                }
                continue;
            }
            
            if (pointOnLineLeft(c, l) != pointOnLineLeft(d, l)) {
                auto p = lineIntersection(l, Line(c, d));
                q.push_back(p);
            }
        }
        
        std::sort(q.begin(), q.end(), [&](auto c, auto d) {
            return dot(c, Point<double>(b) - Point<double>(a)) < dot(d, Point<double>(b) - Point<double>(a));
        });
        
        std::sort(r.begin(), r.end(), [&](auto c, auto d) {
            return dot(c, Point<double>(b) - Point<double>(a)) < dot(d, Point<double>(b) - Point<double>(a));
        });
        
        int t = 0;
        for (int i = 0; i+1 < q.size(); i += 2) {
            e.emplace_back(q[i], 1);
            e.emplace_back(q[i+1], -1);
        }
        for (int i = 0; i+1 < r.size(); i += 2) {
            e.emplace_back(r[i], 1);
            e.emplace_back(r[i+1], -1);
        }
        std::sort(e.begin(), e.end(), [&](auto c, auto d) {
            return dot(c.first, Point<double>(b) - Point<double>(a)) < dot(d.first, Point<double>(b) - Point<double>(a));
        });
        
        for (int i = 0; i < e.size(); i++) {
            if (t > 0) {
                ans += length(e[i].first - e[i-1].first);
            }
            t += e[i].second;
        }
        ans /= 100;
        std::cout << ans << "\n";
    }
    
    return 0;
}