Submission #136047

#	Time	Username	Problem	Language	Result	Execution time	Memory
136047		Minnakhmetov	Triangles (CEOI18_tri)	C++14	100 / 100	1404 ms	4152 KiB

tri

#include<bits/stdc++.h>
#include "trilib.h"
using namespace std;
 
#define ll long long
#define all(aaa) aaa.begin(), aaa.end()
 
int ct = 0;
 
bool is_clockwise2(int a, int b, int c) {
    ct++;
    if (ct > 1000000)
        exit(1);
    return is_clockwise(a, b, c);
}

vector<int> build_hull(vector<int> v, bool inv) {
    sort(v.begin() + 1, v.end(), [=](int x, int y) {
        return is_clockwise2(v[0], x, y) ^ inv;
    });
    vector<int> h;
    for (int x : v) {
        while (h.size() > 1 && !(is_clockwise2(*(h.end() - 2), *(h.end() - 1), x) ^ inv)) {
            h.pop_back();
        }
        h.push_back(x);
    }
    return h;
}
 
vector<int> just_sort(vector<int> v, bool inv) {
    sort(v.begin() + 1, v.end(), [=](int x, int y) {
        return is_clockwise2(v[0], x, y) ^ inv;
    });
    return v;
}
 
const int N = 1e5;
bool ban[N];
int a[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();

    for (int i = 1; i <= n; i++) 
        a[i] = i;

    mt19937 rnd(time(0));

    shuffle(a + 1, a + 1 + n, rnd);
 
    vector<int> v1 = { a[1] }, v2 = { a[1] };
 
    for (int i = 3; i <= n; i++) {
        if (is_clockwise2(a[1], a[2], a[i])) {
            v2.push_back(a[i]);
        }
        else {
            v1.push_back(a[i]);
        }
    }
 
    v1.push_back(a[2]);
    v2.push_back(a[2]);
 
    v1 = build_hull(v1, 0);
    v2 = just_sort(v2, 1);
 
    v2.erase(v2.begin());
    v2.pop_back();
 
    reverse(all(v1));
 
    for (int x : v2) {
        while (v1.size() > 1 && is_clockwise2(*(v1.end() - 2), *(v1.end() - 1), x)) {
            ban[v1.back()] = 1;
            v1.pop_back();
        }
        v1.push_back(x);
    }
 
    reverse(all(v1));
    reverse(all(v2));
 
    for (int x : v2) {
        if (ban[x])
            continue;
        while (v1.size() > 1 && !is_clockwise2(*(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++;
    }
 
    give_answer(ans);
 
    return 0;
}

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