计算几何专项：UVa 11437

求出r、p、q，然后求叉积，取绝对值再除以2就行了。第一次感受到lrj书上模板的威力，感觉好神奇！

#include <iostream>#include <fstream>#include <cstring>#include <cstdio>#include <cmath>using namespace std;struct point{    double x,y;    point(double x=0,double y=0):x(x),y(y){}};point operator+(point a,point b) {return point(a.x+b.x,a.y+b.y);}point operator-(point a,point b) {return point(a.x-b.x,a.y-b.y);}point operator*(point a,double p) {return point(a.x*p,a.y*p);}point operator/(point a,double p) {return point(a.x/p,a.y/p);}const double eps=1e-10;int dcmp(double x){    if(fabs(x)<eps) return 0;    else return x<0?-1:1;}bool operator==(const point& a,const point& b){    return dcmp(a.x-b.x)==0&&dcmp(a.y-b.y)==0;}double cross(point a,point b){    return a.x*b.y-a.y*b.x;}point getpoint(point p,point v,point q,point w){    point u=p-q;    double t=cross(w,u)/cross(v,w);    return p+v*t;}int main(){    freopen("in.txt","r",stdin);    int T;    cin>>T;    while(T--)    {         double x1,y1,x2,y2,x3,y3;         cin>>x1>>y1>>x2>>y2>>x3>>y3;         point a=point(x1,y1);         point b=point(x2,y2);         point c=point(x3,y3);         point e=point((x1+2*x3)/3,(y1+2*y3)/3);         point d=point((x3+2*x2)/3,(y3+2*y2)/3);         point f=point((x2+2*x1)/3,(y2+2*y1)/3);         point r=getpoint(c,f-c,a,d-a);         point p=getpoint(a,d-a,b,e-b);         point q=getpoint(b,e-b,c,f-c);         double area=fabs(cross(p-q,r-q))/2;         printf("%.0f\n",area);    }    return 0;}