hdu 1115 Lifting the Stone【多边形重心】

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题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1115
题意：给你一个多边形，让你求他的重心
解析：多边形重心公式，即把多边形分成多个三角形，然后是三角形的重心的权重和

#include <cmath>#include <algorithm>#include <iostream>#include <cstdio>#include <vector>#include <cstring>using namespace std;const int maxn = 1000000+10;const double eps = 1e-5;struct point{    double x;    double y;    point() {}    point(double _x,double _y)    {        x = _x;        y = _y;    }}a[maxn];double x_mul(point p0,point p1,point p2){    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);}point gravity(int n){    point res = {0,0};    double tmp = 0;    for(int i=0;i<n;i++)    {        double s = x_mul(point(0,0),a[i],a[(i+1)%n]);        tmp += s;        res.x += s*(a[i].x+a[(i+1)%n].x);        res.y += s*(a[i].y+a[(i+1)%n].y);    }    res.x = res.x/tmp/3.0;    res.y = res.y/tmp/3.0;    return res;}int main(void){    int n,t;    cin>>t;    while(t--)    {        scanf("%d",&n);        for(int i=0;i<n;i++)            scanf("%lf %lf",&a[i].x,&a[i].y);        point ans = gravity(n);        printf("%.2f %.2f\n",ans.x,ans.y);    }    return 0;}

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