Submission #386505

#	Time	Username	Problem	Language	Result	Execution time	Memory
386505		phathnv	Planine (COCI21_planine)	C++11	20 / 110	348 ms	24848 KiB

Main

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 1e6 + 7;

struct Fraction{
    ll p, q;
    Fraction(ll _p, ll _q){
        p = _p;
        q = _q;
        assert(q != 0);
        if (q < 0){
            p = -p;
            q = -q;
        }
        ll g = abs(__gcd(p, q));
        p /= g;
        q /= g;
    }
    bool operator == (const Fraction &oth){
        return (p == oth.p && q == oth.q);
    }
    bool operator < (const Fraction &oth) const {
        return ((long double) p * oth.q < (long double) oth.p * q);
    }
};

struct Point{
    int x, y;
    Point(int _x = 0, int _y = 0){
        x = _x;
        y = _y;
    }
};

struct Line{
    ll a, b, c;
    Line(ll _a, ll _b, ll _c){
        a = _a;
        b = _b;
        c = _c;
    }
    Line(const Point &A, const Point &B){
        a = A.y - B.y;
        b = B.x - A.x;
        c = (ll) A.x * B.y - (ll) A.y * B.x;
    }
};

int n, h;
Point p[N];

Fraction findXCoor(const Line &d1, const Line &d2){
    ll D = d1.a * d2.b - d2.a * d1.b;
    ll Dx = -d1.c * d2.b + d2.c * d1.b;
    assert(D != 0);
    return Fraction(Dx, D);
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> h;
    for(int i = 1; i <= n; i++)
        cin >> p[i].x >> p[i].y;

    Line d(0, 1, -h);
    vector<pair<Fraction, Fraction>> segments;
    for(int i = 3; i <= n - 2; i += 2)
        segments.push_back({findXCoor(Line(p[i - 1], p[i]), d), findXCoor(Line(p[i], p[i + 1]), d)});
    sort(segments.begin(), segments.end(), [](const pair<Fraction, Fraction> &a, const pair<Fraction, Fraction> &b){
            return a.second < b.second;
         });
    int answer = 0;
    Fraction lastX = Fraction(-1e18, 1);
    for(auto p : segments)
        if (lastX < p.first){
            answer++;
            lastX = p.second;
        }
    cout << answer;

    return 0;
}

• Subtask 1: 20 / 20
• Subtask 2: 0 / 30
• Subtask 3: 0 / 60