hdu 1115 Lifting the Stone【多边形重心】

#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
using namespace std;
const int maxn = 1000000+10;
const double eps = 1e-5;
struct point
{
double x;
double y;
point() {}
point(double _x,double _y)
{
x = _x;
y = _y;
}
}a[maxn];
double x_mul(point p0,point p1,point p2)
{
return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}
point gravity(int n)
{
point res = {0,0};
double tmp = 0;
for(int i=0;i<n;i++)
{
double s = x_mul(point(0,0),a[i],a[(i+1)%n]);
tmp += s;
res.x += s*(a[i].x+a[(i+1)%n].x);
res.y += s*(a[i].y+a[(i+1)%n].y);
}
res.x = res.x/tmp/3.0;
res.y = res.y/tmp/3.0;
return res;

}
int main(void)
{
int n,t;
cin>>t;
while(t--)
{
scanf("%d",&n);
for(int i=0;i<n;i++)
scanf("%lf %lf",&a[i].x,&a[i].y);
point ans = gravity(n);
printf("%.2f %.2f\n",ans.x,ans.y);
}
return 0;
}