Submission #121409

#	Time	Username	Problem	Language	Result	Execution time	Memory
121409		BThero	Triangles (CEOI18_tri)	C++17	100 / 100	30 ms	2548 KiB

tri

// Why am I so dumb? :c
// chrono::system_clock::now().time_since_epoch().count()
 
//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
 
#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include"trilib.h"
 
#define pb push_back
#define mp make_pair
 
#define all(x) (x).begin(), (x).end()
 
#define fi first
#define se second
 
using namespace std;
using namespace __gnu_pbds;
 
typedef long long ll;   
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
 
const int MAXN = (int)4e4 + 5;
 
vector<int> A, B, V;

int n, idx[MAXN];

bool cmp(int a, int b) {
    return is_clockwise(n, a, b);
}
 
void solve() {
    n = get_n();    

    for (int i = 2; i < n; ++i) {
        if (is_clockwise(n, i, 1)) {
            A.pb(i);
        }
        else {
            B.pb(i);
        }           
    }

    sort(all(A), cmp);
    sort(all(B), cmp);
    int tmp = 0;

    for (int x : A) {
        idx[++tmp] = x;
    }

    idx[++tmp] = 1;

    for (int x : B) {
        idx[++tmp] = x;        
    }

    V.pb(n);
    V.pb(idx[1]);
    tmp = 2;

    for (int i = 2; i <= n - 1; ++i) {
        while (tmp >= 2 && !is_clockwise(V[tmp - 2], V.back(), idx[i])) {
            V.pop_back();
            --tmp;
        }        

        V.pb(idx[i]);
        ++tmp;
    }

    while (V.size() > 3) {
        if (!is_clockwise(V.back(), V.front(), V[1])) {
            V.erase(V.begin());
        }
        else if (!is_clockwise(V[V.size() - 2], V.back(), V.front())) {
            V.pop_back();
        }
        else {
            break;
        }   
    }                  
 
    give_answer(V.size());
}
 
int main() {
    int tt = 1;
 
    while (tt--) {
        solve();
    }
 
    return 0;
}

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