[恢]hdu 2105

2011-12-16 12:01:00

地址：http://acm.hdu.edu.cn/showproblem.php?pid=2105

题意：给3个点的坐标代表一个三角形，求三角形的重心（三条中线的交点）。

mark：计算几何果断在mathematica的帮助下很给力！

代码：

# include <stdio.h>


typedef struct POINT{
    double x, y ;
}POINT ;


typedef struct LINE{
    double a, b, c ; //ax+by+c == 0
}LINE ;


POINT tri[3] ;


POINT Middle(POINT p1, POINT p2)
{
    POINT rtn ;
    rtn.x = (p1.x + p2.x) / 2.0 ;
    rtn.y = (p1.y + p2.y) / 2.0 ;
    return rtn ;
}


LINE GetLine (POINT p1, POINT p2)
{
    LINE rtn ;
    rtn.a = (p1.y - p2.y) ;
    rtn.b = (p2.x - p1.x) ;
    rtn.c = -(p2.x*p1.y - p1.x*p2.y) ;
    return rtn ;
}


POINT Cross(LINE l1, LINE l2)
{
    POINT rtn ;
    double fm = l2.a*l1.b - l1.a*l2.b ;
    rtn.x = (l2.b*l1.c - l1.b*l2.c) / fm ;
    rtn.y = (l1.a*l2.c - l2.a*l1.c) / fm ;
    return rtn ;
}


POINT gao()
{
    POINT p1, p2, rtn ;
    LINE l1, l2 ;
    p1 = Middle(tri[0], tri[1]) ;
    p2 = Middle(tri[1], tri[2]) ;
    l1 = GetLine(p1, tri[2]) ;
    l2 = GetLine(p2, tri[0]) ;
    rtn = Cross(l1, l2) ;
    return rtn ;
}


int main ()
{
    int n, i ;
    POINT pt ;
    while (~scanf ("%d", &n) && n)
    {
        while (n--)
        {
            for (i = 0 ; i< 3 ; i++)
                scanf ("%lf%lf", &tri[i].x, &tri[i].y) ;
            pt = gao() ;
            printf ("%.1lf %.1lf\n", pt.x, pt.y) ;
        }
    }
    return 0 ;
}