oj.uz

답안 #5170

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
5170 2014-02-13T20:57:41 Z cki86201 초록색 삼각형 (YDX13_green) C++
1 / 1
 1008 ms 1356 KB 
#include<stdio.h>
#include<algorithm>
#include<math.h>

typedef long long ll;

const double PI = 3.141592653589793238;

int x[2020], y[2020], ord[2020];
double an[2020];
int n;

bool comp(const int &a,const int &b){return an[a] < an[b];}

void brute()
{
	int i, j, k;
	double ans = 0;
	for(i=3;i<=n;i++){
		for(j=2;j<i;j++){
			for(k=1;k<j;k++){
				ll tmp = (ll)(x[j]-x[i])*(y[k]-y[i])-(ll)(x[k]-x[i])*(y[j]-y[i]);
				if(tmp < 0)tmp = -tmp;
				ans += (double)tmp/n/(n-1)/(n-2)/2;
			}
		}
	}
	printf("%.12f",ans*6);
}

int main()
{
	scanf("%d",&n);
	int i, j;
	for(i=1;i<=n;i++)scanf("%d%d",x+i,y+i);
	if(n<=2)return printf("0")&0;
	if(n<=100){brute();return 0;}
	for(i=1;i<=n;i++)ord[i] = i;
	double ans = 0;
	for(i=1;i<=n;i++){
		for(j=1;j<=n;j++)an[j] = atan2(y[j] - y[i], x[j] - x[i]);
		std::sort(ord+1,ord+1+n,comp);
		ll now[2] = {0,0};
		int t = 1;
		double na = 0;
		for(j=1;j<=n;j++){
			int nj = ord[j];
			if(j>1)na -= fmod(an[nj] - an[ord[j-1]] + 2*PI, 2*PI);
			while(na < PI){
				now[0] += x[ord[t]] - x[i];
				now[1] += y[ord[t]] - y[i];
				na += fmod(an[ord[t%n+1]] - an[ord[t]] + 2*PI, 2*PI);
				t = t%n + 1;
			}
			now[0] -= x[nj] - x[i], now[1] -= y[nj] - y[i];
			ans += (double)now[1] * (x[nj] - x[i]) - (double)now[0] * (y[nj] - y[i]);
		}
	}
	printf("%.12f",ans/n/(n-1)/(n-2));
	return 0;
}

Subtask #1
1.0 / 1.0

# 결과 실행 시간 메모리 Grader output
1 Correct 0 ms 1356 KB Output is correct
2 Correct 0 ms 1356 KB Output is correct
3 Correct 0 ms 1356 KB Output is correct
4 Correct 0 ms 1356 KB Output is correct
5 Correct 0 ms 1356 KB Output is correct
6 Correct 0 ms 1356 KB Output is correct
7 Correct 0 ms 1356 KB Output is correct
8 Correct 0 ms 1356 KB Output is correct
9 Correct 0 ms 1356 KB Output is correct
10 Correct 0 ms 1356 KB Output is correct
11 Correct 176 ms 1356 KB Output is correct
12 Correct 340 ms 1356 KB Output is correct
13 Correct 220 ms 1356 KB Output is correct
14 Correct 900 ms 1356 KB Output is correct
15 Correct 88 ms 1356 KB Output is correct
16 Correct 872 ms 1356 KB Output is correct
17 Correct 52 ms 1356 KB Output is correct
18 Correct 140 ms 1356 KB Output is correct
19 Correct 224 ms 1356 KB Output is correct
20 Correct 0 ms 1356 KB Output is correct
21 Correct 1004 ms 1356 KB Output is correct
22 Correct 1000 ms 1356 KB Output is correct
23 Correct 996 ms 1356 KB Output is correct
24 Correct 996 ms 1356 KB Output is correct
25 Correct 1008 ms 1356 KB Output is correct
26 Correct 1000 ms 1356 KB Output is correct
27 Correct 1004 ms 1356 KB Output is correct
28 Correct 996 ms 1356 KB Output is correct
29 Correct 996 ms 1356 KB Output is correct
30 Correct 1000 ms 1356 KB Output is correct
31 Correct 0 ms 1356 KB Output is correct