Submission #95997

#	Time	Username	Problem	Language	Result	Execution time	Memory
95997		youngyojun	Triangles (CEOI18_tri)	C++11	100 / 100	29 ms	2372 KiB

tri

#include "trilib.h"
#include <bits/stdc++.h>
#define eb emplace_back
#define sz(V) ((int)(V).size())
#define befv(V) ((V)[sz(V)-2])
#define allv(V) ((V).begin()),((V).end())
#define sorv(V) sort(allv(V))
#define univ(V) (V).erase(unique(allv(V)),(V).end())
using namespace std;

int ccw(int a, int b, int c) {
	if(a == b || b == c || c == a) return 0;
	return is_clockwise(a, b, c) ? 1 : -1;
}

vector<int> LV, RV;

int N;

void f(vector<int> &V) {
	sort(V.begin()+1, V.end(), [&](int a, int b) {
		return 0 < ccw(V[0], a, b);
	});
	vector<int> T;
	for(int v : V) {
		for(; 1 < sz(T) && ccw(befv(T), T.back(), v) <= 0; T.pop_back());
		T.eb(v);
	}
	swap(V, T);
}

int main() {
	N = get_n();

	LV.eb(1); RV.eb(2);
	for(int i = 3; i <= N; i++)
		(0 < ccw(1, 2, i) ? LV : RV).eb(i);
	f(LV); f(RV);

	int al = 0, ar = 0, bl = 0, br = 0, ln = sz(LV), rn = sz(RV);
	for(bool flag;;) {
		flag = false;
		for(; 0 < ccw(LV[al], RV[ar], LV[(al+1)%ln]); al=(al+1)%ln) flag = true;
		for(; 0 < ccw(LV[al], RV[ar], RV[(ar-1+rn)%rn]); ar=(ar-1+rn)%rn) flag = true;
		if(!flag) break;
	}
	for(bool flag;;) {
		flag = false;
		for(; ccw(LV[bl], RV[br], LV[(bl-1+ln)%ln]) < 0; bl=(bl-1+ln)%ln) flag = true;
		for(; ccw(LV[bl], RV[br], RV[(br+1)%rn]) < 0; br=(br+1)%rn) flag = true;
		if(!flag) break;
	}

	vector<int> Ans;
	for(int i = br;; i = (i+1)%rn) {
		Ans.eb(RV[i]);
		if(i == ar) break;
	}
	for(int i = al;; i = (i+1)%ln) {
		Ans.eb(LV[i]);
		if(i == bl) break;
	}

	sorv(Ans); univ(Ans);
	give_answer(sz(Ans));
	return 0;
}

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