POJ3304 segment(线段交判断)

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#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <vector>using namespace std;const double inf = 1e-8;int dcmp(double x){    if(fabs(x) < 1e-8)            return 0;    if(x < 0)   return -1;    return 1;//1为正，-1为负，0为等}struct point{    double x , y;    point(double x = 0,double y= 0):x(x),y(y){}/************************************/};typedef point Vector;point operator + (const Vector &a , const Vector &b){    return Vector(a.x + b.x,a.y + b.y);}point operator - (const Vector &a , const Vector &b){    return Vector(a.x - b.x,a.y - b.y);}point operator * (const Vector &a , const double &p){    return Vector(a.x * p,a.y * p);}point operator / (const Vector &a , const double &p){    return Vector(a.x / p,a.y / p);}bool operator > (const point &a,const point &b){return a.x > b.x;}bool operator == (const point &a,const point &b){    return dcmp(a.x - b.x) == 0 && dcmp(a.y - b.y) ==0;};double cross(const Vector &a ,const Vector &b){    return (a.x * b.y - a.y * b.x);}double cross(point a,point b,point o){    return (a.x-o.x)*(b.y-o.y)-(a.y-o.y)*(b.x-o.x);}double dot(const Vector &a,const Vector &b){    return (a.x * a.y + b.x * b.y);}struct segment{    point s,e;    segment(point a = point(0,0),point b = point(0,0)){    s = a;e = b;    }};point pnt[300];segment seg[200];int cnt;int cases;int lnum ;bool OnSegment(point p,point a1,point a2){  return dcmp(cross(a1-p,a2-p))==0&&dcmp(dot(a1-p,a2-p))<0; //线段包含端点时改成<=}bool cancross(segment &a,segment &b){    //跨立实验    double c1 = cross(b.e - a.e , a.s - a.e) ,        c2 = cross(b.s - a.e , a.s - a.e),        c3 = cross(a.e - b.e , b.s - b.e),        c4 = cross(a.s - b.e , b.s - b.e);    if(dcmp(c1)*dcmp(c2) < 0 && dcmp(c1)*dcmp(c2) < 0)            return true;    if(OnSegment(a.e,b.e,b.s)||OnSegment(a.s,b.e,b.s)||OnSegment(b.e,a.e,a.s)||OnSegment(b.s,a.e,a.s))                return true;            return false;}bool judge(segment p){    point a(0,0) ,b(0,0);    a = p.e;    b = p.s;    if(abs(a.x-b.x)<inf&&abs(a.y-b.y)<inf) return false;    for(int i=0;i<lnum;++i)    {        if(cross(a,b,seg[i].s)*cross(a,b,seg[i].e)>inf)           return false;    }    return true;}int main(){    double x1,y1,x2,y2;    scanf("%d",&cases);    while(cases --)    {        memset(seg,0,sizeof(seg));        memset(pnt,0,sizeof(pnt));        bool flag = false;        scanf("%d",&lnum);        for(int i = 0; i < lnum ;i++){            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);            pnt[2*i] = point(x1,y1);            pnt[2*i+1] = point(x2,y2);            seg[i] = segment(pnt[2*i],pnt[2*i+1]);        }        int i,j;        if(lnum ==1 )   flag =true;        for(i = 0; i <= 2*lnum-2 && flag == false;i++)            for(j = i ; j <= 2*lnum-2 && flag == false;j++)                if(judge(segment(pnt[i],pnt[j])))                    flag = true;        if(flag)                printf("Yes!\n");        else                printf("No!\n");    }    return 0;}
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