oj.uz

답안 #5176

# 제출 시각 아이디 문제 언어 결과 실행 시간 메모리
5176 2014-02-13T23:15:47 Z cki86201 초록색 삼각형 (YDX13_green) C++
0 / 1
 420 ms 1448 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];}

inline ll ccw(int a,int b,int c)
{
	return (ll)(x[b]-x[a]) * (y[c]-y[a]) - (ll)(x[c]-x[a]) * (y[b]-y[a]);
}

double solve(int u)
{
	if(u <= 2)return 0;
	double ret = 0;
	int i;
	for(i=1;i<=u;i++)ord[i] = i;
	for(i=1;i<=u;i++)an[i] = atan2(y[i] - y[u], x[i] - x[u]);
	std::sort(ord+1,ord+1+u,comp);
	int t = (ord[1] == u)?2:1;
	ll now[2] = {0,0};
	for(i=1;i<=u;i++){
		int ni = ord[i];
		if(ni == u)continue;
		now[0] -= x[ni] - x[u], now[1] -= y[ni] - y[u];
		while(ord[t] == u || t == i)now[0] += x[ord[t]] - x[u], now[1] += y[ord[t]] - y[u], t = t%u + 1;
		while(t!=i && ccw(u,ni,ord[t]) > 0){
			now[0] += x[ord[t]] - x[u];
			now[1] += y[ord[t]] - y[u];
			t = t%u + 1;
			if(ord[t] == u)t = t%u + 1;
		}
		ret += (double)now[1] * (x[ni] - x[u]) - (double)now[0] * (y[ni] - y[u]);
	}
	return ret + solve(u-1);
}

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;
	printf("%.12f\n",solve(n)*3/n/(n-1)/(n-2));
	return 0;
}

Subtask #1
0.0 / 1.0

# 결과 실행 시간 메모리 Grader output
1 Correct 0 ms 1352 KB Output is correct
2 Correct 0 ms 1352 KB Output is correct
3 Correct 0 ms 1352 KB Output is correct
4 Correct 0 ms 1352 KB Output is correct
5 Correct 0 ms 1352 KB Output is correct
6 Correct 0 ms 1352 KB Output is correct
7 Correct 0 ms 1352 KB Output is correct
8 Correct 0 ms 1352 KB Output is correct
9 Correct 0 ms 1352 KB Output is correct
10 Correct 0 ms 1352 KB Output is correct
11 Correct 72 ms 1352 KB Output is correct
12 Correct 144 ms 1360 KB Output is correct
13 Correct 92 ms 1352 KB Output is correct
14 Correct 376 ms 1432 KB Output is correct
15 Correct 36 ms 1352 KB Output is correct
16 Correct 364 ms 1432 KB Output is correct
17 Correct 16 ms 1352 KB Output is correct
18 Correct 56 ms 1352 KB Output is correct
19 Correct 88 ms 1352 KB Output is correct
20 Correct 0 ms 1352 KB Output is correct
21 Correct 416 ms 1448 KB Output is correct
22 Correct 420 ms 1444 KB Output is correct
23 Correct 420 ms 1448 KB Output is correct
24 Correct 416 ms 1448 KB Output is correct
25 Correct 416 ms 1448 KB Output is correct
26 Correct 416 ms 1448 KB Output is correct
27 Correct 416 ms 1448 KB Output is correct
28 Correct 416 ms 1444 KB Output is correct
29 Correct 412 ms 1444 KB Output is correct
30 Correct 416 ms 1448 KB Output is correct
31 Incorrect 0 ms 1352 KB Output isn't correct