poj 1269 Intersecting Lines（计算几何：线段相交）

给出两条线段，问对应哪三种情况：

不相交，重合，相交于一点

代码如下:

/* ***********************************************

Author        :yinhua

Email         :yinwoods@163.com

File Name     :poj1269.cpp

Created Time  :2014年12月02日 星期二 16时49分10秒

************************************************ */

#include <cmath>
#include <cstdio>
#include <string>
#include <cstring>
#include <iostream>
#include <algorithm>
#define MAXN 1010
#define eps 1e-6
#define LL long long
using namespace std;

double ansx, ansy;

struct Point {
    double x, y;
    Point() {}
    Point(double _x, double _y) {
        x = _x, y = _y;
    }
    Point operator -(const Point &b) const {
        return Point(x-b.x, y-b.y);
    }
    double operator *(const Point &b) const {
        return x*b.x+y*b.y;
    }
    double operator ^(const Point &b) const {
        return x*b.y-y*b.x;
    }
};

int sgn(double x) {
    if(fabs(x) < eps) return 0;
    if(x < 0) return -1;
    return 1;
}

struct Line {
    Point s, e;
    Line() {}
    Line(Point _s, Point _e) {
        s = _s, e = _e;
    }
    pair<Point, int> operator &(const Line &b) const {
        Point res = s;
        if(sgn((s-e)^(b.s-b.e)) == 0) {
            if(sgn((b.s-s)^(b.e-s)) == 0)
                return make_pair(res, 0);
            else return make_pair(res, 1);
        }
        double t = ((s-b.s)^(b.s-b.e))/((s-e)^(b.s-b.e));
        res.x += (e.x-s.x)*t;
        res.y += (e.y-s.y)*t;
        return make_pair(res, 2);
    }
};

int main() {

    int n;
    while(~scanf("%d", &n)) {
        puts("INTERSECTING LINES OUTPUT");
        Line l1, l2;
        while(n--) {
            scanf("%lf%lf%lf%lf", &l1.s.x, &l1.s.y, &l1.e.x, &l1.e.y);
            scanf("%lf%lf%lf%lf", &l2.s.x, &l2.s.y, &l2.e.x, &l2.e.y);
            pair<Point, int> ans = l1 & l2;
            if(ans.second == 2) printf("POINT %.2lf %.2lf\n", ans.first.x, ans.first.y);
            else if(ans.second == 0) puts("LINE");
            else puts("NONE");
        }
        puts("END OF OUTPUT");
    }
    return 0;
}