Gathers no Moss - BIO 2022 Round 2

#include <iostream>
#include <set>
#include <vector>
#include <tuple>
#include <algorithm>

using namespace std;

void setIO() {
    #ifndef EREKLE
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
}

struct Point {
    int x, y;
    Point(int x0, int y0): x(x0), y(y0){}
    Point(){}
};

typedef pair<Point, Point> Slope;

struct Command {
    int x, type;
    Slope slope;
    bool operator < (const Command &c2) const {
        return pair<int, int>(x, type) < pair<int, int>(c2.x, c2.type);
    }
    Command(int x2, int type2, Slope slope2): x(x2), type(type2), slope(slope2){}
};

int main() {
    setIO();
    int x = 0; // x value used to compare slopes
    auto higher = [&x](const Slope &s1, const Slope &s2) {
        double y1 = s1.first.y + (double)(s1.second.y - s1.first.y) * (x-s1.first.x)/(s1.second.x-s1.first.x);
        double y2 = s2.first.y + (double)(s2.second.y - s2.first.y) * (x-s2.first.x)/(s2.second.x-s2.first.x);
        return y1 > y2;
    };

    int n; cin >> n;
    vector<Command> commands; // x, type (0=start, 1=finish), slope
    Slope curSlope{{0, 0}, {0, 0}};
    for (int i = 0; i < n; ++i) {
        Slope s;
        cin >> s.first.x >> s.first.y >> s.second.x >> s.second.y;
        if (!s.first.x && !s.first.y) curSlope = s;
        commands.emplace_back(s.first.x, 0, s);
        commands.emplace_back(s.second.x, 1, s);
    }
    sort(commands.begin(), commands.end());

    int slopeCount = 1; // slopes traversed
    set<Slope, decltype(higher)> activeSlopes(higher);
    for (int ci = 0; ci < (int)commands.size(); ++ci) {
        Command &c = commands[ci];
        x = c.x;
        if (c.type == 0) {
            activeSlopes.insert(c.slope);
        } else {
            activeSlopes.erase(c.slope);
            if (ci+1 == (int)commands.size() || commands[ci+1].x > c.x) {
                if (curSlope.second.x == c.x) {
                    set<Slope, decltype(higher)>::iterator it = activeSlopes.upper_bound(curSlope);
                    if (it == activeSlopes.end()) break;
                    curSlope = *it;
                    ++slopeCount;
                }
            }
        }
    }
    cout << slopeCount << endl;
    cout << curSlope.second.x << ' ' << curSlope.second.y << endl;
    return 0;
}