POJ 1410 Intersection(线段相交)

判断线段是否与矩形有交集。。

刚开始看成直线错了好几发。。

#include <cstdio>#include <cmath>#include <algorithm>using namespace std;typedef struct point {    double x;    double y;}point;typedef struct v {    point start;    point end;}v;const double eps = 1e-8;point rec[4], seg[2];double crossProduct(v* v1, v* v2){    v vt1, vt2;    double result = 0;    vt1.start.x = 0;    vt1.start.y = 0;    vt1.end.x = v1->end.x - v1->start.x;    vt1.end.y = v1->end.y - v1->start.y;    vt2.start.x = 0;    vt2.start.y = 0;    vt2.end.x = v2->end.x - v2->start.x;    vt2.end.y = v2->end.y - v2->start.y;    result = vt1.end.x * vt2.end.y - vt1.end.y * vt2.end.x;    return result;}bool onLine(point pi, point pj, point Q){    v v1, v2;    v1.start = v2.start = Q;    v1.end = pi;    v2.end = pj;    if(crossProduct(&v1, &v2) == 0)        return true;    return false;}double multi(point p1, point p2, point p0)  //used for Across{    return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);}int Across(v v1, v v2)  //segmentCross,use functions: multi(){    if(max(v1.start.x,v1.end.x) >= min(v2.start.x, v2.end.x) &&       max(v2.start.x,v2.end.x) >= min(v1.start.x, v1.end.x) &&       max(v1.start.y,v1.end.y) >= min(v2.start.y, v2.end.y) &&       multi(v2.start, v1.end, v1.start) * multi(v1.end, v2.end, v1.start) > 0 &&       multi(v1.start, v2.end, v2.start) * multi(v2.end, v1.end, v2.start) > 0)        return 1;    else        return 0;}bool onSegment(point Pi, point Pj, point Q) //Pi, Pj, Q are all different points{//same slopes or same x-coordinates or same y-coordinates    if((Q.x - Pi.x) * (Pj.y - Pi.y) == (Pj.x - Pi.x) * (Q.y - Pi.y) &&         min(Pi.x, Pj.x) <= Q.x && Q.x <= max(Pi.x, Pj.x)&&         min(Pi.y, Pj.y) <= Q.y && Q.y <= max(Pi.y, Pj.y))  //determine that Q is "between" Pi and Pj         return true;    else        return false;}bool inRectangle(point p, point a, point b){    if(p.x >= a.x && p.x <= b.x && p.y >= b.y && p.y <= a.y)        return true;    return false;}int main(){    //freopen("1", "r", stdin);    int t;    for(scanf("%d", &t); t--;) {        bool ok = false;        double x1, y1, x2, y2;        v v1, v2;        scanf("%lf%lf%lf%lf", &seg[0].x, &seg[0].y, &seg[1].x, &seg[1].y);        scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2);        rec[1].x = min(x1, x2);        rec[1].y = max(y1, y2);        rec[3].x = max(x1, x2);        rec[3].y = min(y1, y2);        rec[2].y = rec[1].y;        rec[2].x = rec[3].x;        rec[0].x = rec[1].x;        rec[0].y = rec[3].y;        v1.start = seg[0];        v1.end = seg[1];        for(int i = 0; i < 2; i++) {            if(inRectangle(seg[i], rec[1], rec[3])) {                ok = true;                break;            }        }        for(int i = 0;!ok && i < 4; i++) {            v2.start = rec[i];            v2.end = rec[(i+1)%4];            if(onSegment(seg[0], seg[1], rec[i]) || onSegment(rec[i], rec[(i+1)%4], seg[0]) ||               onSegment(rec[i], rec[(i+1)%4], seg[1]) || Across(v1, v2)) {                ok = true;                break;            }        }        puts(ok ? "T" : "F");    }    return 0;}