hdu 1115 Lifting the Stone 多边形的重心

 

#include<iostream>
#include<cmath>
using namespace std;
struct point{
    double x,y;
    point (double xx=0,double yy=0){
        x=xx;  y=yy;
    }
    double operator *(point b){
        return x*b.y-y*b.x;
    }
}p[1000001];
int main()
{
    int T,N,i;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&N);
        for(i=0;i<N;i++)
            scanf("%lf%lf",&p[i].x,&p[i].y);
        p[N].x=p[0].x;  p[N].y=p[0].y;    
        double area=0;
        point re;
        for(i=0;i<N;i++)
        {
            area+=p[i]*p[i+1];
            re.x+=(p[i].x + p[i+1].x)* (p[i]*p[i+1]);
            re.y+=(p[i].y + p[i+1].y)* (p[i]*p[i+1]);
        }
        area/=2;
        re.x /= 6*area;
        re.y /= 6*area;
        printf("%.2lf %.2lf\n",re.x,re.y);
    }
    return 0;
}