poj 1296 Noise Effect(判断线段相交，并求交点)

//以下为原blog搬迁过来的内容

【题目大意】：给出n组数据，每组数据四个数描述两条直线，判断直线重合，平行，或者相交。

【解题思路】：按照重合，平行，相交的顺序依次判断就是。主要是为了测试计算几何模版

【代码】：

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <vector>#include <queue>#include <cmath>#include <string>#include <cctype>#include <map>#include <iomanip>                   using namespace std;                   #define eps 1e-8#define pi acos(-1.0)#define inf 1<<30#define pb push_back#define lc(x) (x << 1)#define rc(x) (x << 1 | 1)#define lowbit(x) (x & (-x))#define ll long longstruct Point{    double x,y;    Point() {}    Point (double a,double b)    {        x=a,y=b;    }}point[8];struct Line{    Point a,b;    Line() {}    Line(Point x,Point y)    {        a=x,b=y;    }}line[2];inline int sig(double k) {    return k < -eps ? -1 : k > eps;}inline double det(double x1, double y1, double x2, double y2){    return x1 * y2 - x2 * y1;}inline double xmult(Point o, Point a, Point b){    return det(a.x - o.x, a.y - o.y, b.x - o.x, b.y - o.y);}void getline(const Point &x, const Point &y, double &a, double &b, double &c){    a = y.y - x.y;    b = x.x - y.x;    c = y.x * x.y - x.x * y.y;}inline bool parallel(Line u,Line v){    return sig((u.a.x-u.b.x)*(v.a.y-v.b.y)-(v.a.x-v.b.x)*(u.a.y-u.b.y))==0;}inline bool sameline(Line u,Line v){    if (sig(xmult(u.a,v.a,v.b))==0 && sig(xmult(u.b,v.a,v.b))==0)        return true;    else return false;}Point intersect(double a1, double b1, double c1, double a2, double b2, double c2){    Point ret;    ret.y = (a1 * c2 - c1 * a2) / (b1 * a2 - a1 * b2);    if (sig(a2) == 0)  ret.x = -(b1 * ret.y + c1) / a1;    else ret.x = -(b2 * ret.y + c2) / a2;    return ret;}int main(){    int T;    scanf("%d",&T);    printf("INTERSECTING LINES OUTPUT\n");    while (T--)    {        double p,q;        for (int i=0; i<=3; i++)        {            scanf("%lf%lf",&p,&q);            point[i]=Point(p,q);        }        line[0]=Line(point[0],point[1]);        line[1]=Line(point[2],point[3]);        double a1,a2,b1,b2,c1,c2;        getline(line[0].a,line[0].b,a1,b1,c1);        getline(line[1].a,line[1].b,a2,b2,c2);        if (sameline(line[0],line[1])==true) printf("LINE\n");        else        {            if (parallel(line[0],line[1])==true) printf("NONE\n");            else            {                Point p1;                p1=intersect(a1,b1,c1,a2,b2,c2);                printf("POINT %.2lf %.2lf\n",p1.x,p1.y);            }        }    }    printf("END OF OUTPUT\n");    return 0;}