Submission #136028

#	Time	Username	Problem	Language	Result	Execution time	Memory
136028		Minnakhmetov	Triangles (CEOI18_tri)	C++14	75 / 100	3083 ms	4860 KiB

tri

#include<bits/stdc++.h>
#include "trilib.h"
using namespace std;
 
#define ll long long
#define all(aaa) aaa.begin(), aaa.end()

deque<int> build_hull(deque<int> v, bool inv) {
    sort(v.begin() + 1, v.end(), [=](int x, int y) {
        return is_clockwise(v[0], x, y) ^ inv;
    });
    deque<int> h;
    for (int x : v) {
        while (h.size() > 1 && !(is_clockwise(*(h.end() - 2), *(h.end() - 1), x) ^ inv)) {
            h.pop_back();
        }
        h.push_back(x);
    }
    return h;
}

const int N = 1e5;
bool ban[N];

signed main() {
#ifdef HOME
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int n = get_n();

    deque<int> v1 = { 1 }, v2 = { 1 };

    for (int i = 3; i <= n; i++) {
        if (is_clockwise(1, 2, i)) {
            v2.push_back(i);
        }
        else {
            v1.push_back(i);
        }
    }

    v1.push_back(2);
    v2.push_back(2);

    v1 = build_hull(v1, 0);
    v2 = build_hull(v2, 1);

    // for (int i : v1)
    //     cout << i << " ";
    // cout << "\n";
    // for (int i : v2)
    //     cout << i << " ";

    // return 0;

    v2.pop_front();
    v2.pop_back();

    for (int x : v2) {
        while (v1.size() > 1 && is_clockwise(v1[1], v1[0], x)) {
            ban[v1.front()] = 1;
            v1.pop_front();
        }
        v1.push_front(x);
    }


    reverse(all(v2));



    for (int x : v2) {
        while (v1.size() > 1 && !is_clockwise(*(v1.end() - 2), *(v1.end() - 1), x)) {
            ban[v1.back()] = 1;
            v1.pop_back();
        }
        v1.push_back(x);
    }


    sort(all(v1));
    v1.erase(unique(all(v1)), v1.end());

    int ans = 0;
    for (int i : v1) {
        if (!ban[i])
            ans++;
    }

    cout << ans;


    return 0;
}

• Subtask 1: 15 / 15
• Subtask 2: 20 / 20
• Subtask 3: 20 / 20
• Subtask 4: 20 / 20
• Subtask 5: 0 / 25