Submission #680181

#	Time	Username	Problem	Language	Result	Execution time	Memory
680181		jhwest2	Triangles (CEOI18_tri)	C++17	100 / 100	21 ms	2076 KiB

tri

#include "trilib.h"
#include <bits/stdc++.h>
using namespace std;
 
const int N = 40040;
int n, inv[N];
 
int main() {
    n = get_n();
 
    int u = 1, v = 2;
    vector<int> a, b;
 
    for (int i = 3; i <= n; i++) {
        if (!is_clockwise(u, v, i))
            a.push_back(i);
        else
            b.push_back(i);
    }
    if (a.size() > b.size()) {
        swap(a, b);
        swap(u, v);
    }
 
    sort(a.begin(), a.end(), [&](int i, int j) {
        return is_clockwise(u, i, j);
    });
 
    deque<int> hull;
    hull.push_back(u);
    for (int x : a) {
        while (hull.size() >= 2) {
            if (!is_clockwise(hull[hull.size() - 2], hull.back(), x))   
                hull.pop_back();
            else
                break;
        }
        hull.push_back(x);
    }
    hull.push_back(v);
    
    sort(b.begin(), b.end(), [&](int i, int j) {
        return is_clockwise(v, i, j);
    });
 
    for (int x : b) {
        while (hull.size() >= 2) {
            if (!is_clockwise(hull[hull.size() - 2], hull.back(), x))
                hull.pop_back();
            else
                break;
        }
        hull.push_back(x);
    }

    for (int i = 0; i < N; i++) {
        int x = hull.front(); hull.pop_front();
        while (hull.size() >= 2) {
            if (!is_clockwise(hull[hull.size() - 2], hull.back(), x))
                hull.pop_back();
            else
                break;
        }
        hull.push_back(x);
    }
 
    give_answer((int)hull.size());
}

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