zoj 2105 Lifting the Stone

题意   裸的计算几何  求多边形重心；

#include<iostream>
#include<stdio.h>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;

double a,b,c,d,e,f;
double mix( double x,double y,double xx,double yy ){return x*yy - xx*y;}
int main( )
{
    int N,T; scanf("%d",&T);
    while( T-- )
    {
        scanf("%d",&N);  scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
        double sumx = 0,sumy = 0,suma = 0;
        for( int i = 3; i <= N; i++ )
        {
            scanf("%lf%lf",&e,&f);
            double area = mix(e-a,f-b,c-a,d-b)/2.0;
            sumx += (( a+c+e )*area);
            sumy += (( b+d+f )*area);
            suma += area;
            c = e; d = f;
        }
        sumx = int(sumx/suma/3.0*100000.0);
        sumy = int(sumy/suma/3.0*100000.0);
        printf("%.2lf %.2lf
",sumx/100000.0,sumy/100000.0);
    }
    return 0;
}