ZOJ1648 Circuit Board（线段相交）

裸的判断线段相交

#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cmath>
#include <ctime>
#include <vector>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <algorithm>
using namespace std;
#define eps 1e-12
#define MAXN 2005
#define INF 1000000007
#define MAX(a,b) (a > b ? a : b)
#define MIN(a,b) (a < b ? a : b)
#define mem(a) memset(a,0,sizeof(a))

struct Point{
    double x,y;
    Point(double x=0, double y=0):x(x),y(y){}
};

double Cross(Point A, Point B) { return A.x*B.y - A.y*B.x;}//叉积

int N;
struct LINE
{
    Point s, e;
} Line[MAXN];

int main()
{
    while(~scanf("%d", &N))
    {
        for(int i=0;i<N;i++)
        {
            scanf("%lf%lf%lf%lf", &Line[i].s.x, &Line[i].s.y, &Line[i].e.x, &Line[i].e.y);
        }
        int ok = 1;
        for(int i=0;i<N && ok;i++)
        {
            Point Pi = Point(Line[i].e.x-Line[i].s.x, Line[i].e.y-Line[i].s.y);
            for(int j=i+1;j<N && ok; j++)
            {
                double c1 = Cross(Point(Line[j].s.x-Line[i].s.x, Line[j].s.y-Line[i].s.y), Pi);
                double c2 = Cross(Point(Line[j].e.x-Line[i].s.x, Line[j].e.y-Line[i].s.y), Pi);
                if(c1 * c2 < 0)
                {
                    Point Pj = Point(Line[j].e.x-Line[j].s.x, Line[j].e.y-Line[j].s.y);
                    c1 = Cross(Point(Line[i].s.x-Line[j].s.x, Line[i].s.y-Line[j].s.y), Pj);
                    c2 = Cross(Point(Line[i].e.x-Line[j].s.x, Line[i].e.y-Line[j].s.y), Pj);
                    if (c1 * c2 < 0) ok = 0;
                }
            }
        }
        printf("%s
",ok?"ok!":"burned!");
    }
    return 0;
}