hdu1115 Lifting the Stone（几何，求多边形重心模板题）

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题目链接：http://acm.hdu.edu.cn/showproblem.php?

pid=1115

Lifting the Stone

2
4
5 0
0 5
-5 0
0 -5
4
1 1
11 1
11 11
1 11

0.00 0.00
6.00 6.00

题意：就是给你一个多边行的点的坐标。求此多边形的重心。

一道求多边形重心的模板题。

代码例如以下：

//求多边形中心(採用吉林大学模板)
#include <cstdio>
#include <cmath>
#include <cstring>

struct point 
{
	double x, y; 
}PP[1000047];

point bcenter(point pnt[], int n)
{
	point p, s;
	double tp, area = 0, tpx = 0, tpy = 0;
	p.x = pnt[0].x; 
	p.y = pnt[0].y;
	for (int i = 1; i <= n; ++i) 
	{ // point: 0 ~ n-1
		s.x = pnt[(i == n) ? 0 : i].x;
		s.y = pnt[(i == n) ? 0 : i].y;
		tp = (p.x * s.y - s.x * p.y);
		area += tp / 2;
		tpx += (p.x + s.x) * tp;
		tpy += (p.y + s.y) * tp;
		p.x = s.x; p.y = s.y;
	}
	s.x = tpx / (6 * area); s.y = tpy / (6 * area);
	return s;
}

int main()
{
	int N, t;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%d",&N);
		for(int i = 0; i < N; i++)
		{
			scanf("%lf%lf",&PP[i].x,&PP[i].y);
		}
		point ss = bcenter(PP,N);
		printf("%.2lf %.2lf\n",ss.x ,ss.y);
	}
	return 0;
}

模版例如以下：

struct point 
{
	double x, y; 
};

point bcenter(point pnt[], int n)
{
	point p, s;
	double tp, area = 0, tpx = 0, tpy = 0;
	p.x = pnt[0].x; 
	p.y = pnt[0].y;
	for (int i = 1; i <= n; ++i) 
	{ // point: 0 ~ n-1
		s.x = pnt[(i == n) ? 0 : i].x;
		s.y = pnt[(i == n) ?
 0 : i].y;
		tp = (p.x * s.y - s.x * p.y);
		area += tp / 2;
		tpx += (p.x + s.x) * tp;
		tpy += (p.y + s.y) * tp;
		p.x = s.x; p.y = s.y;
	}
	s.x = tpx / (6 * area); s.y = tpy / (6 * area);
	return s;
}