HDU1115 --多边形重心求解

第二个模板,有公式的.

#include<stdio.h>
#include<stdlib.h>
typedef struct point
{
	double x,y;
}point;
point p[10001];
double cal(int i,int j)
{
	return p[i].x*p[j].y-p[j].x*p[i].y;
}
int main()
{
	int t,n,i;
	double result,cx,cy;
	while(scanf("%d",&n)!=EOF)
	{
		while(n--)
		{
			scanf("%d",&t);
			for(i=0;i<t;i++)
			{
				scanf("%lf%lf",&p[i].x,&p[i].y);
			}
			p[t].x=p[0].x;p[t].y=p[0].y;
			result = 0;
			for(i=0;i<t;i++)
				result += cal(i,i+1);
			result /= 2;
			cx = cy = 0;
			for (i = 0; i < t; i++)
			{
				cx += (p[i].x + p[i+1].x)*cal(i, i+1);
				cy += (p[i].y + p[i+1].y)*cal(i, i+1);
			}
			cx /= 6*result;
			cy /= 6*result;
			printf("%.2lf %.2lf\n",cx,cy);
		}
	}
	return 0;
}