Submission #5170

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
5170	2014-02-13T20:57:41 Z	cki86201	초록색 삼각형 (YDX13_green)	C++	1 / 1	1008 ms	1356 KB

C

#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

#	Verdict	Execution time	Memory	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