POJ 2826 || an easy problem ?!(未AC，呵呵~

今日未AC，来日再战，头脑混沌。

#include<cstdio>#include<cmath>#include<algorithm>using namespace std;const double eps = 1e-8;int dcmp( double x ){    if( fabs(x)<eps)        return 0;    return x < 0 ? -1: 1;}//================= 点结构 ===============struct pnode{    double x,y;    pnode( double a=0.0,double b=0.0):x(a),y(b){}    // X乘重载    double operator ^ (const pnode &b)const    {        return x*b.y - b.x*y;    }    pnode operator - ( const pnode &b)const    {        return pnode( x-b.x,    y-b.y);    }    pnode operator * (const double p)const    {        return pnode( x*p,   y*p );    }    pnode operator + (const pnode&b)const    {        return pnode( x+b.x, y+b.y );    }    bool operator == (const pnode&b)const    {        return dcmp( x-b.x )== 0 && dcmp( y-b.y )==0;    }    bool operator < (const pnode&b)const    {        return x < b.x || ( dcmp( x-b.x )==0 && y<b.y );    }    bool operator > (const pnode&b)const    {        return x > b.x || ( dcmp( x-b.x )==0 && y>b.y );    }};//================ 线结构 ==============typedef pnode myvec;struct pline{    pnode st,ed;//st：起始点 ed：终点    myvec vec;//向量    pline(){}    pline(pnode a,pnode b):st(a),ed(b)    {        vec = pnode(b-a);    }    void pread()    {        scanf("%lf %lf %lf %lf",&st.x,&st.y,&ed.x,&ed.y);        if( ed.y > st.y)            swap(st,ed);        vec = pnode(ed-st);    }};double cross( pnode p0,pnode p1,pnode p2){    return (p1-p0) ^ (p2-p0);}double cross(pline a,pline b){    return (a.ed-a.st)^(b.ed-b.st);}/*    点乘：        dot(v,w) == 二者长度乘积再乘上他们夹角的余弦        夹角：从 v 到 w 逆时针旋转的角*/double dot( myvec v,myvec w){    return v.x*w.x + v.y*w.y;}bool seg_inter_seg(pline a,pline b){    return        max( a.st.x, a.ed.x) >=  min( b.st.x, b.ed.x)    &&        max( b.st.x, b.ed.x) >=  min( a.st.x, a.ed.x)    &&        max( a.st.y, a.ed.y) >=  min( b.st.y, b.ed.y)    &&        max( b.st.y, b.ed.y) >=  min( a.st.y, a.ed.y)    &&//以上端点判断        dcmp(cross( a.st, a.ed, b.st ))*dcmp(cross( a.st, a.ed, b.ed ))<=0    &&  dcmp(cross( b.st, b.ed, a.st ))*dcmp(cross( b.st, b.ed, a.ed ))<=0;}pnode get_line_inter_point(pline v,pline w){    pline u (w.st,v.st);    double t = cross( w,u )/cross(v,w);    return v.st + (v.ed-v.st) * t;}bool seg_inter_line(pline line,pline seg){    return ( dcmp( cross( seg.st,line.st,line.ed ) ) * dcmp( cross( seg.ed,line.st,line.ed) ) )<=0;}int check(pline a,pline b,pnode &p1,pnode &p2){    pnode getit;    pline ay (a.st,pnode(a.st.x+100,a.st.y));    pline by (b.st,pnode(b.st.x+100,a.st.y));    if( seg_inter_line(ay,b))    {        pline ax(a.st,pnode(a.st.x,10000 ));        if( seg_inter_seg(ax,b))            return 0;        p1 = get_line_inter_point(ay,b);        p2 = a.st;        return 1;    }    if( seg_inter_line(by,a))    {        pline bx(b.st,pnode(b.st.x,10000 ));        if( seg_inter_seg(bx,a))            return 0;        p1 = get_line_inter_point(by,a);        p2 = b.st;        return 1;    }    return 0;}pline a,b;pline yl (pnode(0,0),pnode(0,100));int main(){    int cas;    scanf("%d",&cas);    while( cas-- )    {        a.pread();        b.pread();        if( dcmp ( cross(a,b)) == 0 || dcmp(dot(yl.vec,a.vec))==0 || dcmp(dot(yl.vec,b.vec))==0 )        {            puts("0.00");            //puts("1");            continue;        }        pnode p = get_line_inter_point(a,b),p1,p2;        int s = check(a,b,p1,p2);        if( s==0 )        {            puts("0.00");            //puts("2");            continue;        }        double area = fabs ( cross(p,p1,p2)*0.5 );        printf("%0.2f\n",area);    }    return 0;}