Submission #121993

#	Time	Username	Problem	Language	Result	Execution time	Memory
121993		_7_7_	Triangles (CEOI18_tri)	C++14	100 / 100	28 ms	2428 KiB

tri

#include <bits/stdc++.h>                                           
#include "trilib.h"

#define int long long	
//#pragma GCC optimize("Ofast")
//#pragma comment(linker, "/stack:200000000")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4")

#define file(s) freopen(s".in","r",stdin); freopen(s".out","w",stdout);                                          
#define forev(i, b, a) for(int i = (b); i >= (a); --i)	    
#define forn(i, a, b) for(int i = (a); i <= (b); ++i)
#define sz(s) (int)s.size()
#define all(x) x.bg, x.en                                                                    
#define pb push_back
#define ppb pop_back
#define mp make_pair
#define rbg rbegin()
#define bg begin()
#define en end()
#define s second
#define f first                                               
	
   
using namespace std;                  
   
   
typedef pair < long long, long long > pll;    
typedef pair < int, int > pii;
typedef unsigned long long ull;         
typedef vector < pii > vpii;
typedef vector < int > vi;
typedef long double ldb; 
typedef long long ll;  
typedef double db;                            
						               
				
const int dx[] = {1, -1, 0, 0}, dy[] = {0, 0, 1, -1}, block = 265;	
const pii base = mp(1171, 3307), Mod = mp(1e9 + 7, 1e9 + 9);  
const int inf = 1e9, N = 1e6 + 11, mod = 1e9 + 7;
const db eps = 1e-12, pi = 3.14159265359; 
const ll INF = 1e18;	


int n, st[N];
vi v1, v2;

bool cmp (int x, int y) { //sort by tga
	return is_clockwise(1, x, y);
}
/*

bool is_clockwise (int x, int y, int z) {
	cout << "? " << x << ' ' << y << ' ' << z << endl;
	int res;
	cin >> res;
	return res;
}                                     

int get_n () {
	cout << "n ?\n";
	int n;
	cin >> n;
	return n;
}

void give_answer (int x) {
	cout << "! " << x << endl;
}*/




main () {                                  
	ios_base :: sync_with_stdio(0);
//	cin.tie(0);                                        
//	cout.tie(0);
	n = get_n();

	forn (i, 3, n)
		if (is_clockwise(1, 2, i))	
			v1.pb(i);
		else
			v2.pb(i);



	sort(all(v1), cmp);
	sort(all(v2), cmp);
	reverse(all(v1));
	v1.pb(2);
	reverse(all(v2));
	for (auto x : v2)
		v1.pb(x);
	reverse(all(v1));

	int Sz = 0;
	st[++Sz] = 1;
	for (auto x : v1) {
		while (Sz > 1 && !is_clockwise(st[Sz - 1], st[Sz], x))
			--Sz;
		st[++Sz] = x;
	}	
/*
	forn (i, 1, Sz)
		cout << st[i] << ' ';
	cout << endl;*/


	int pr = 1, suff = Sz;
	bool ok = 1;
	while (ok && suff - pr + 1 >= 3) { //triangle is always convex		
		ok = 0;
		if (!is_clockwise(st[suff], st[pr], st[pr + 1])) 
			++pr, ok = 1;                                  		
		else if (is_clockwise(st[pr], st[suff], st[suff - 1]))
			--suff, ok = 1;
	}
	give_answer(suff - pr + 1);
	return 0;
}

Compilation message (stderr)

tri.cpp:73:7: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main () {                                  
       ^

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