[POJ 1385] Lifting the Stone （计算几何）

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <cmath>
 5 using namespace std;
 6 typedef long long LL;
 7 #define EPS 1e-8
 8 #define X first
 9 #define Y second
10 
11 typedef struct _POINT{ // 用pair<double,double>会MLE！！
12     double first;
13     double second;
14 }POINT;
15 
16 typedef POINT VECTOR;
17 double operator*(VECTOR x,VECTOR y){
18     double res;
19     res = x.X*y.Y-x.Y*y.X ;
20     return res;
21 }
22 VECTOR operator-(POINT x,POINT y){
23     VECTOR res;
24     res.X = x.X - y.X ;
25     res.Y = x.Y - y.Y ;
26     return res;
27 }
28 
29 const int MAX_N = 1000001;
30 int T,N;
31 POINT pt[MAX_N];
32 
33 POINT getCenter(POINT points[],int n){
34     POINT res;
35     double area,areamulx,areamuly;
36     area = 0.0; areamulx = 0.0 ; areamuly = 0.0;
37     for(int i=1;i<n-1;i++){
38         VECTOR v1 = points[i]-points[0];
39         VECTOR v2 = points[i+1]-points[i]; // 后面如果fabs会损失精度。。
40         double tarea = v1 * v2 / 2.0;
41         area += tarea;
42         areamulx += (points[0].X+points[i].X+points[i+1].X)*tarea;
43         areamuly += (points[0].Y+points[i].Y+points[i+1].Y)*tarea;
44     }
45     res.X = areamulx / (3.0*area);
46     res.Y = areamuly / (3.0*area);
47     return res;
48 }
49 
50 int main(){
51     scanf("%d",&T);
52     while( T-- ){
53         scanf("%d",&N);
54         for(int i=0;i<N;i++){
55             scanf("%lf%lf",&pt[i].X,&pt[i].Y);
56         }
57         POINT ans = getCenter(pt,N);
58         printf("%.2lf %.2lf\n",ans.X+EPS,ans.Y+EPS);
59     }
60     return 0;
61 }