[POJ1269]Intersecting Lines (计算几何)

题目链接：http://poj.org/problem?id=1269

题意：给两条直线，判断这两条直线是平行中的重合还是相交。

一切尽在不言中：

#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstring>
#include <climits>
#include <complex>
#include <fstream>
#include <cassert>
#include <cstdio>
#include <bitset>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <ctime>
#include <set>
#include <map>
#include <cmath>

using namespace std;

const double eps = 1e-8;

typedef struct Point {
    double x;
    double y;
    Point() {}
    Point(double xx, double yy) : x(xx), y(yy) {}
    Point operator +(const Point& b) const { return Point(x+b.x, y+b.y); }
    Point operator -(const Point& b) const { return Point(x-b.x, y-b.y); }
    double operator ^(const Point& b) const { return x * b.y - y * b.x; }
    double operator *(const Point& b) const { return x * b.x + y * b.y; }
}Point;

typedef struct Line {
    Point u;
    Point v;
    Line() {}
    Line(Point uu, Point vv) : u(uu), v(vv) {}
}Line;

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

double xmulti(Point p0, Point p1, Point p2) {
    return (p1 - p0) ^ (p2 - p0);
}

double dist(Point a, Point b) {
    return sqrt((b-a)*(b-a));
}

double intersect(Line l1, Line l2) {
    return sgn(xmulti(l2.u, l1.u, l1.v))*sgn(xmulti(l2.v, l1.u, l1.v))<=0;
}

double ex1, ey1, ex2, ey2;
double ex3, ey3, ex4, ey4;

pair<Point, int> check(Line l1, Line l2) {
    Point ans = l1.u;
    if(sgn((l1.u-l1.v)^(l2.u-l2.v)) == 0) {
        if(sgn((l2.u-l1.u)^(l2.v-l1.u)) == 0) {
            return pair<Point, int>(ans, 0);//chonghe
        }
        else {            
            return pair<Point, int>(ans, 1);//pingxing
        }
    }
    double t = ((l1.u - l2.u) ^ (l2.u - l2.v)) / ((l1.u - l1.v) ^ (l2.u - l2.v));
    ans.x += (l1.v.x - l1.u.x) * t;
    ans.y += (l1.v.y - l1.u.y) * t;
    return pair<Point, int>(ans, 2);//jiaodian ans
}

int main() {
    // freopen("in", "r", stdin);
    int T;
    scanf("%d", &T);
    printf("INTERSECTING LINES OUTPUT
");
    while(T--) {
        scanf("%lf %lf %lf %lf", &ex1, &ey1, &ex2, &ey2);
        scanf("%lf %lf %lf %lf", &ex3, &ey3, &ex4, &ey4);
        Line l1 = Line(Point(ex1, ey1), Point(ex2, ey2));
        Line l2 = Line(Point(ex3, ey3), Point(ex4, ey4));
        pair<Point, int> ans = check(l1, l2);
        if(ans.second == 0) {
            printf("LINE
");
        }
        else if(ans.second == 1) {
            printf("NONE
");
        }
        else {
            printf("POINT %.2f %.2f
", ans.first.x, ans.first.y);
        }
    }
    printf("END OF OUTPUT
");
    return 0;
}