POJ_1410

    几个需要注意的地方：

    ①给出的矩形顶点的坐标需要自己重新排下序再使用，看discuss说所谓的top等并不是严格指上方，只是一个相对的参考，所以要重新排下序再用。

    ②因为题目里面说了矩形的内部也算矩形的一部分，所以线段在矩形内部是认为和矩形相交的。

    ③在判断线段与矩形四个边是否有交点时，要注意对非规范相交的判定，当线段和边共线且不相交时叉积也为0。

#include
     
       #include
      
        #define zero 1e-8 double xs, ys, xe, ye, xl, yl, xr, yr, x1[5], y1[5], x2[5], y2[5]; double det(double x1, double y1, double x2, double y2) {
   return x1 * y2 - y1 * x2; } double fabs(double x) {
   return x < 0 ? -x : x; } double min(double x, double y) {
   return x < y ? x : y; } double max(double x, double y) {
   return x > y ? x : y; } int dcmp(double x) {
   if(fabs(x) < zero) return 0; if(x < 0) return -1; return 1; } int onseg(double x, double y, double x1, double y1, double x2, double y2) {
   if(fabs(x2 - x1) < fabs(y2 - y1)) return dcmp((y - y2) * (y - y1)) <= 0; else return dcmp((x - x2) * (x - x1)) <= 0; } void solve() {
   int i, j, k; double t1, t2, t3, t4;     x1[0] = xl, y1[0] = yr, x2[0] = xr, y2[0] = yr;     x1[1] = xl, y1[1] = yr, x2[1] = xl, y2[1] = yl;     x1[2] = xl, y1[2] = yl, x2[2] = xr, y2[2] = yl;     x1[3] = xr, y1[3] = yr, x2[3] = xr, y2[3] = yl; for(i = 0; i < 4; i ++)     {
           t1 = det(x2[i] - x1[i], y2[i] - y1[i], xs - x1[i], ys - y1[i]);         t2 = det(x2[i] - x1[i], y2[i] - y1[i], xe - x1[i], ye - y1[i]);         t3 = det(xe - xs, ye - ys, x1[i] - xs, y1[i] - ys);         t4 = det(xe - xs, ye - ys, x2[i] - xs, y2[i] - ys); if(dcmp(t1) * dcmp(t2) < 0 && dcmp(t3) * dcmp(t4) < 0)         {
               printf("T\n"); return ;         } if((dcmp(t1) == 0 && onseg(xs, ys, x1[i], y1[i], x2[i], y2[i])) || (dcmp(t2) == 0 && onseg(xe, ye, x1[i], y1[i], x2[i], y2[i])) || (dcmp(t3) == 0 && onseg(x1[i], y1[i], xs, ys, xe, ye)) ||(dcmp(t4) == 0 && onseg(x2[i], y2[i], xs, ys, xe, ye)))         {
               printf("T\n"); return ;         }     }     printf("F\n"); } int main() {
   int i, t; double x;     scanf("%d", &t); while(t --)     {
           scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &xs, &ys, &xe, &ye, &xl, &yl, &xr, &yr); if(xl > xr)             x = xl, xl = xr, xr = x; if(yl < yr)             x = yl, yl = yr, yr = x; if((xs < xr && xs > xl && ys < yl && ys > yr) || (xe < xr && xe > xl && ye < yl && ye > yr))             printf("T\n"); else             solve();     } return 0; }