Submission #538349

#	Time	Username	Problem	Language	Result	Execution time	Memory
538349		siewjh	Planine (COCI21_planine)	C++17	20 / 110	233 ms	32148 KiB

Main

#include <bits/stdc++.h>
typedef long double ld;
typedef long long ll;
using namespace std;
int nums; ll h;
struct pt{
    ll x, y;
};
struct hull{
    vector<pt> v;
    bool ccw(pt a, pt b, pt c){
        return a.x * (b.y - c.y) + b.x * (c.y - a.y) + c.x * (a.y - b.y) > 0;
    }
    void insert(pt p){
        while (!v.empty() && v.back().y <= p.y) v.pop_back();
        v.push_back(p);
    }
    pair<ll, ll> query(pt p){
        while (v.size() >= 2 && ccw(v[v.size() - 2], v.back(), p)) v.pop_back();
        auto a = v.back();
        return {(p.x - a.x) * (h - a.y) + a.x * (p.y - a.y), p.y - a.y};
    }
};
bool cmpfrac(pair<ll, ll> a, pair<ll, ll> b){
    return a.first * b.second < b.first * a.second;
}
bool cmp(pair<pair<ll ,ll>, pair<ll, ll>> a, pair<pair<ll ,ll>, pair<ll, ll>> b){
    return cmpfrac(a.second, b.second);
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    cin >> nums >> h;
    pt vec[nums];
    for (int i = 0; i < nums; i++) cin >> vec[i].x >> vec[i].y;
    int valley = (nums - 3) / 2;
    pair<pair<ll, ll>, pair<ll, ll>> range[valley];
    hull left;
    for (int i = 1, j = 0; i < nums - 1; i++){
        if (i % 2) left.insert(vec[i]);
        else {
            range[j].first = left.query(vec[i]);
            j++;
        }
    }
    hull right;
    for (int i = nums - 2, j = valley - 1; i >= 1; i--){
        if (i % 2) right.insert(vec[i]);
        else {
            range[j].second = right.query(vec[i]);
            j--;
        }
    }
    sort(range, range + valley, cmp);
    int ans = 0; pair<ll, ll> last_pos;
    for (int i = 0; i < valley; i++)
        if (i == 0 || cmpfrac(last_pos, range[i].first)){
            ans++;
            last_pos = range[i].second;
        }
    cout << ans;
}

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