Intersection(poj1401线段和矩形相交)

题意：给你一条线段和一个矩形，判断线段是否和矩形相交，线段在矩形当中也算相交，并且矩形的坐标不是左上右下

思路：这道题知道自己模板错了，

1.线段相交判看是否有线段的端点在线段上，就是说要特判点在线段上

2.点在直线上要包括点在线段的两个端点，即dcmp(Cross(b-a,p-a)) == 0 && dcmp(Dot(b-p,a-p)) < 0 || (p == a) || (p == b);

剩下的就是细心加细心

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;struct Point{    double x,y;    Point(double x = 0,double y = 0):x(x),y(y){}};typedef Point Vector;Vector operator + (Vector a, Vector b) { return Vector(a.x+b.x,a.y+b.y) ;}Vector operator - (Vector a, Vector b) { return Vector(a.x-b.x,a.y-b.y) ;}Vector operator * (Vector a,double p) { return Vector(a.x*p,a.y*p) ;}Vector operator / (Vector a,double p) { return Vector(a.x/p,a.y/p) ;}double Dot(Vector a,Vector b) { return a.x*b.x + a.y*b.y ;}double Length(Vector a) { return sqrt(Dot(a,a)) ;}double Cross(Vector a, Vector b) { return a.x*b.y - a.y*b.x ;}const double eps = 1e-5;int dcmp(double x){    if(fabs(x) < eps) return 0;    else return x < 0 ? -1 : 1;}bool operator == (Point a,Point b){    return dcmp(a.x-b.x) == 0&& dcmp(a.y-b.y) == 0;}bool operator < (Point a,Point b){    return a.x < b.x || (a.x == b.x && a.y < b.y);}double Min(double a,double b){    return a < b ? a : b;}double Max(double a,double b){    return a > b ? a  : b;}bool Onsegment(Point p,Point a,Point b){    return dcmp(Cross(b-a,p-a)) == 0 && dcmp(Dot(b-p,a-p)) < 0 || (p == a) || (p == b);}bool SegmentIntersection(Point a,Point b,Point c,Point d){    double d1 = Cross(b-a,c-a),d2 = Cross(b-a,d-a),d3 = Cross(d-c,a-c),d4 = Cross(d-c,b-c);    if(dcmp(d1)*dcmp(d2) < 0 && dcmp(d3)*dcmp(d4) < 0) return true;    else if(dcmp(d1) == 0 && Onsegment(c,a,b) ) return true;    else if(dcmp(d2) == 0 && Onsegment(d,a,b) ) return true;    else if(dcmp(d3) == 0 && Onsegment(a,c,d) ) return true;    else if(dcmp(d4) == 0 && Onsegment(b,c,d) ) return true;    else return false;}bool pointInpoly(Point p,Point a,Point b,Point c,Point d){    double d1 = Cross(b-a,p-a);    double d2 = Cross(d-c,p-c);    double d3 = Cross(c-b,p-b);    double d4 = Cross(a-d,p-d);    return dcmp(d1)*dcmp(d2) > 0 && dcmp(d3)*dcmp(d4) > 0;}struct Line{    Point s,e;    Line(Point s = 0,Point e = 0) :s(s),e(e){}};int main(){    int n;    scanf("%d",&n);    while(n--)    {        double x,y,x1,y1,x2,y2,x3,y3;        scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x,&y,&x1,&y1,&x2,&y2,&x3,&y3);        Point a,b,c,d;        if(x3 < x2 &&  y2 < y3)        {            int t = x2;     x2 = x3;       x3 = t;            t = y2;     y2 = y3;     y3 = t;             a = Point(x2,y2),b = Point(x2,y3),c = Point(x3,y3),d = Point(x3,y2);        }        else if(x2 < x3 && y2 > y3)        {             a = Point(x2,y2),b = Point(x2,y3),c = Point(x3,y3),d = Point(x3,y2);        }        else if(x2 > x3 && y2 > y3)        {             a = Point(x2,y2),b = Point(x3,y2),c = Point(x3,y3),d = Point(x2,y3);        }        else if(x3 > x2 && y3 > y2)        {             a = Point(x3,y3),b = Point(x2,y3),c = Point(x2,y2),d = Point(x3,y2);        }        else            a = Point(x3,y3),b = Point(x2,y3),c = Point(x2,y2),d = Point(x3,y2);        if(SegmentIntersection(Point(x,y),Point(x1,y1),a,b))            printf("T\n");        else  if(SegmentIntersection(Point(x,y),Point(x1,y1),b,c))            printf("T\n");        else  if(SegmentIntersection(Point(x,y),Point(x1,y1),c,d))            printf("T\n");        else  if(SegmentIntersection(Point(x,y),Point(x1,y1),d,a))            printf("T\n");        else if( pointInpoly(Point(x,y),a,b,c,d) && pointInpoly(Point(x1,y1),a,b,c,d))            printf("T\n");        else            printf("F\n");    }    return 0;}