poj 1269 Intersecting Lines 线段相交 平行 重合

利用斜率；斜率相同 在判断是否等同的 如果不是则平行；斜率不同 求交点；#include <iostream>#include <cstdio>#include <cmath>using namespace std;const double eps = 1e-9;//注意精度；const double inf = 1e10;double x1, y, x2, y2, x3, y3, x4, y4;bool dx(double x1, double x2){    return abs(x1-x2) < eps;//两点相同；}double xl(double x1, double y1, double x2, double y2)//求斜率；{    if(dx(x1, x2)) return inf;//平行y轴 无斜率；    return (y1-y2)/(x1-x2);}int main(){    int t;    cout << "INTERSECTING LINES OUTPUT" << endl;    scanf("%d", &t);    while(t--)    {        scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1, &y, &x2, &y2, &x3, &y3, &x4, &y4);        double k1 = xl(x1, y, x2, y2), k2 = xl(x3, y3, x4, y4);        if(dx(k1, k2))        {            if((dx(x1, x2) && dx(x1, x3)) ||(dx((y-k1*x1), (y3-k2*x3)))) cout << "LINE" << endl;            else cout << "NONE" << endl;        }        else        {            double b1 = y-k1*x1, b2 = y3-k2*x3;            printf("POINT %.2lf %.2lf\n", (b1-b2)/(k2-k1), k1*(b1-b2)/(k2-k1)+b1);        }    }    cout << "END OF OUTPUT" << endl;    return 0;}