nyoj-3-多边形重心问题（求多边形面积和中心）

题目链接

 /*
     Name:nyoj-3-多边形重心问题
     Copyright:
     Author:
     Date: 2018/4/26 21:25:41
     Description:
     ACM国际大学生程序设计竞赛 算法与实现的模板
 */
 #include <iostream>
 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 const double eps = 1e-;
 int cmp(double x) {
     if (fabs(x) < eps) return ;
     if (x > )return ;
     return -;
 }
 //point
 struct point {
     double x, y;
     point (){}
     point (double a, double b):x(a), y(b) {    }
     void input() {
         scanf("%lf %lf", &x, &y);
     }
     friend point operator - (const point &a, const point &b) {
         return point(a.x-b.x, a.y-b.y);
     }
     friend point operator + (const point &a, const point &b) {
         return point(a.x+b.x, a.y+b.y);
     }
     friend point operator * (const double &a, const point &b) {
         return point (a * b.x, a*b.y);
     }
     friend point operator / (const point &a, const double &b) {
         return point (a.x / b, a.y /b);
     }
     friend bool operator == (const point &a, const point &b) {
         return (cmp(a.x - b.x) ==  && cmp(a.y - b.y) == );
     }
 };
 double det(const point &a, const point &b) {
     return a.x * b.y - a.y * b.x;
 }
 //polygon
 const int MAXN = ;
 struct polygon {
     int n;
     point a[MAXN];
     polygon(){
     }
     double area() {
         double sum = ;
         a[n] = a[];
         for (int i=; i<n; i++) sum+=det(a[i+], a[i]);
         return sum/;
     }
     point MassCenter() {
         point ans = point(, );
         if (cmp(area()) == ) return ans;
         a[n] = a[];
         for (int i=; i<n; i++) ans = ans + det(a[i+], a[i]) * (a[i] + a[i+]) ;
         return ans / area()/;
     }
 };
 int main()
 {
     int n;
     cin>>n;
     while (n--) {
         int m;
         cin>>m;
         polygon pgon;
         pgon.n = m;
         for (int i=; i<m; i++) {
             cin>>pgon.a[i].x>>pgon.a[i].y;
         }
         point ans = pgon.MassCenter();
         printf("%.3f %.3f\n", pgon.area(), ans.x+ans.y);
     }
     return ;
 }