hdu 1115 Lifting the Stone （求重心）

#include<iostream>#include<iomanip>using namespace std;typedef struct point{    double x,y;    point(double x=0.0,double y=0.0):x(x),y(y){}}vector;point p[1000010],c;vector operator - (point a,point b) {return vector(a.x-b.x,a.y-b.y);}point operator + (point a,point b) {return point(a.x+b.x,a.y+b.y);}point operator / (point a,int b) {return point(a.x/b,a.y/b);}point operator * (point a,double b) {return point(a.x*b,a.y*b);}double cross(vector a,vector b){    return a.x*b.y-a.y*b.x;}double area2(point a,point b,point c) {return cross(b-a,c-a);}int main(){    int i,t,n;    double s,m;    point tt;    cin>>t;    while(t--)    {        cin>>n;        s=0.0;tt.x=0.0;tt.y=0.0;        for(i=0;i<n;i++)        {            cin>>p[i].x>>p[i].y;        }        for(i=2;i<n;i++)        {            m=0.5*area2(p[0],p[i-1],p[i]);s+=m; //三角形的品質與面積成正比            c=(p[0]+p[i]+p[i-1])/3; //三角形的重心            tt=tt+(c*m);        }        tt=tt/s;        cout<<fixed<<setprecision(2)<<tt.x<<" "<<fixed<<setprecision(2)<<tt.y<<endl;    }    return 0;}