POJ 2826 An Easy Problem?!

题目链接:POJ2826

以后题目都不贴算了。。难弄又没啥意义，链接上面也有。

这题就是一个几何细节题 有很多情况 

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<queue>using namespace std;struct Point{    double x,y;    Point(double a=0.0,double b=0.0){x=a;y=b;}    Point operator-(Point a){return Point(x-a.x,y-a.y);}    Point operator+(Point a){return Point(x+a.x,y+a.y);}    Point operator/(double a){return Point(x/a,y/a);}    Point operator*(double a){return Point(x*a,y*a);}    bool operator==(Point a){return x==a.x&&y==a.y;}}a[2],b[2],c[2],cro;struct Line{    double a,b,c;    Line(Point p0=Point(1.0,1.0),Point p1=Point())    {        a=p1.y-p0.y;b=p0.x-p1.x;        c=(p0.y-p1.y)*p0.x+(p1.x-p0.x)*p0.y;    }    Point intersect(Line l)    {        return Point(1.0*(b*l.c-l.b*c)/(l.b*a-b*l.a),                     1.0*(l.a*c-a*l.c)/(a*l.b-l.a*b));    }}l1,l2,l3;bool in(Point p1,Point p2,Point p3){    return p1.x<=max(p2.x,p3.x) && p1.x>=min(p2.x,p3.x) &&           p1.y<=max(p2.y,p3.y) && p1.y>=min(p2.y,p3.y);}bool can(Point p1,Point p2,Point p3){    if(p1.x<=max(p2.x,p3.x) && p1.x>=min(p2.x,p3.x)) return 1;    if((p2.y-p1.y)*(p3.x-p1.x)>(p3.y-p1.y)*(p2.x-p1.x)) return p3.x>p2.x;    else return p2.x>p3.x;}double xmult(Point p0,Point p1,Point p2){    return (p1.x-p0.x)*(p2.y-p0.y)-(p1.y-p0.y)*(p2.x-p0.x);}int main(){    freopen("1.txt","r",stdin);    int t;    scanf("%d",&t);    while(t--)    {        for(int i=0;i<2;i++)            scanf("%lf%lf",&a[i].x,&a[i].y);        for(int i=0;i<2;i++)            scanf("%lf%lf",&b[i].x,&b[i].y);        if(abs(a[0].y-a[1].y)<1e-6 || abs(b[0].y-b[1].y)<1e-6) puts("0.00");        else        {            l1=Line(a[0],a[1]);l2=Line(b[0],b[1]);            if(abs(l1.a*l2.b-l1.b*l2.a)<1e-6) puts("0.00");            else            {                cro=l1.intersect(l2);                if(in(cro,a[0],a[1])==0 || in(cro,b[0],b[1])==0) puts("0.00");                else                {                    if(a[1].y>cro.y) swap(a[1],a[0]);                    if(b[1].y>cro.y) swap(b[1],b[0]);                    if(can(cro,a[0],b[0])==0) puts("0.00");                    else                    {                        if(a[0].y<b[0].y) b[0]=l2.intersect(Line(Point(0.0,a[0].y),Point(1.0,a[0].y)));                        else a[0]=l1.intersect(Line(Point(0.0,b[0].y),Point(1.0,b[0].y)));                        printf("%.2f\n",abs(xmult(cro,a[0],b[0]))/2);                    }                }            }        }    }    return 0;}