Submission #121190

#	Time	Username	Problem	Language	Result	Execution time	Memory
121190		BThero	Triangles (CEOI18_tri)	C++17	0 / 100	2 ms	428 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;

int pivot;

bool cmp(int a, int b) {
    return is_clockwise(pivot, a, b);    
}

void printVec(vector<int> V) {
    printf("Hull is:");

    for (int x : V) {
        printf(" %d", x);
    }

    printf("\n");
}

void solve() {
    int n = get_n();
    int ans = n;        

    vector<int> pivots;

    for (int i = 1; i <= n; ++i) {
        pivots.pb(i);
    }

    while (pivots.size() > 2) {
        int a = pivots[0], b = pivots[1];
        vector<int> nxt;

        for (int i = 2; i < pivots.size(); ++i) {
            if (!is_clockwise(a, b, pivots[i])) {
                nxt.pb(pivots[i]);
            }        
        }

        if (nxt.empty()) {
            pivots = {a, b};
        }
        else {
            pivots = nxt;
        }
    }

    for (int tmp : pivots) {
        pivot = tmp;
        vector<int> idx, V;

        for (int j = 1; j <= n; ++j) {
            if (j != pivot) {
                idx.pb(j);
            }
        }    

        sort(all(idx), cmp);
        V.pb(pivot);
        V.pb(idx[0]);

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

            V.pb(idx[i]);
        }

        bool good = 1;

        for (int i = 0; i < V.size(); ++i) {
            good &= is_clockwise(V[i], V[(i + 1) % V.size()], V[(i + 2) % V.size()]);
        }

        if (good) {
            ans = min(ans, (int)V.size());
            //printVec(V);
            //give_answer(V.size());
            //return;
        }
    }

    give_answer(ans);
}

int main() {
    int tt = 1;

    while (tt--) {
        solve();
    }

    return 0;
}

Compilation message (stderr)

tri.cpp: In function 'void solve()':
tri.cpp:58:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 2; i < pivots.size(); ++i) {
                         ~~^~~~~~~~~~~~~~~
tri.cpp:86:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 1; i < idx.size(); ++i) {
                         ~~^~~~~~~~~~~~
tri.cpp:96:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < V.size(); ++i) {
                         ~~^~~~~~~~~~

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