POJ 1269

题意：
    判断直线间位置关系： 相交，平行，重合

include <iostream>
#include <cstdio>
using namespace std;
struct Point
{
    int x , y;
    Point(int a = 0, int b = 0) :x(a), y(b) {}
};
struct Line
{
    Point s, e;
    int a, b, c;//a>=0
    Line() {}
    Line(Point s1,Point e1) : s(s1), e(e1) {}
    void Coefficient()//get a,b,c 
    {
        a = e.y - s.y;
        b = s.x - e.x;
        c = e.x * s.y - s.x * e.y;
        if(a < 0) a = -a,b = -b,c = -c;
    }
};
int Line_Inter_Line(Line & l1,Line & l2, double &x,double &y)//直线 平行: 0, 相交：1, 重合: 2 
{
    l1.Coefficient();
    l2.Coefficient();
    if(l1.a * l2.b == l2.a * l1.b)
    {
        if(l1.b * l2.c != l1.c * l2.b || l1.a * l2.c != l1.c * l2.a) return 0;
        else return 2;
    }
    x =(double) - (l1.c * l2.b - l2.c * l1.b) / (l1.a * l2.b - l2.a * l1.b);// (c1b2-c2b1)/(a1b2-a2b1)
    y =(double)   (l1.c * l2.a - l2.c * l1.a) / (l1.a * l2.b - l2.a * l1.b);// (c1a2-c2a1)/(a1b2-a2b1)
    return 1;
}
int n;
int main()
{
    puts("INTERSECTING LINES OUTPUT");
    scanf("%d", &n);
    while (n--)
    {
        Point p1, p2, p3, p4;
        double x, y;
        scanf("%d%d%d%d%d%d%d%d",&p1.x, &p1.y, &p2.x, &p2.y, &p3.x, &p3.y, &p4.x, &p4.y);
        Line l1 = Line(p1, p2), l2 = Line(p3, p4);
        int f = Line_Inter_Line(l1, l2, x, y);
        if (f == 0) puts("NONE");
        else if (f == 2) puts("LINE");
        else printf("POINT %.2f %.2f
", x, y);
    }
    puts("END OF OUTPUT");
}