Submission #945340

#	Time	Username	Problem	Language	Result	Execution time	Memory
945340		Aiperiii	Triangles (CEOI18_tri)	C++14	20 / 100	1 ms	600 KiB

tri

#include <bits/stdc++.h>
//#include "trilib.h"
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(),x.end()
using namespace std;
static int n;
static long long *x, *y;
static int queries=0;

static void init() {
    static int is_inited=0;
    if (is_inited)
        return;
    is_inited=1;
    assert(scanf("%d", &n)==1);
    x=(long long*)malloc((n+1)*sizeof(long long));
    y=(long long*)malloc((n+1)*sizeof(long long));
    for (int i=1; i<=n; i++)
        assert(scanf("%lld%lld", &x[i], &y[i])==2);
}

int get_n() {
    init();
    return n;
}

int is_clockwise(int a, int b, int c) {
    init();
    assert(a>=1 && a<=n);
    assert(b>=1 && b<=n);
    assert(c>=1 && c<=n);
    assert(a!=b && a!=c && b!=c);
    queries++;
        if(queries == 1000 * 1000 + 1)
            printf("Too many queries!");
    return (x[b]-x[a])*(y[c]-y[a])-(x[c]-x[a])*(y[b]-y[a])<0;
}

void give_answer(int s) {
    init();
    printf("%d\n", s);
}
bool sorting(int x,int y) {
    return is_clockwise(x,1,y);
 }
signed main(){
    int n=get_n();
    vector <int> v1,v2;
    for(int i=3;i<=n;i++){
        if(is_clockwise(1,2,i))v1.pb(i);
        else v2.pb(i);
    }
    sort(all(v1),sorting);
    sort(all(v2),sorting);
    reverse(all(v1));
    vector <int> hull2={1,2},hull1={1,2};
    for(auto x : v2){
        while(hull2.size()>1 && is_clockwise(hull2[hull2.size()-2],hull2[hull2.size()-1],x)){
            hull2.pop_back();
        }
        hull2.pb(x);
    }
    for(auto x : v1){
        while(hull1.size()>1 && !is_clockwise(hull1[hull1.size()-2],hull1[hull1.size()-1],x)){
            hull1.pop_back();
        }
        hull1.pb(x);
    }
    hull2.pb(hull2.front());
    hull2.erase(hull2.begin());
    for(int i=hull1.size()-1;i>=2;i--){
        int x=hull1[i];
        while(hull2.size()>1 && is_clockwise(hull2[hull2.size()-2],hull2[hull2.size()-1],x)){
            hull2.pop_back();
        }
        hull2.pb(x);
    }
    while(hull2.size()>1 && is_clockwise(hull2[hull2.size()-2],hull2[hull2.size()-1],hull2[0])){
        hull2.pop_back();
    }
    reverse(all(hull2));
    while(hull2.size()>1 && !is_clockwise(hull2[hull2.size()-2],hull2[hull2.size()-1],hull2[0])){
        hull2.pop_back();
    }
    give_answer(hull2.size());
}

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