ZOJ 1648 线段相交

题意：

是否存在规范相交

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>

#define N 2020
#define EPS 1e-4
//规范相交 
using namespace std;

struct PO
{
    double x,y;
};

struct LI
{
    PO a,b;
}li[N];

int n;

inline int doublecmp(double x)
{
    if(x>EPS) return 1;
    else if(x<-EPS) return -1;
    return 0;
}

inline double cross(PO &a,PO &b,PO &c)
{
    return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
}

inline double dot(PO &a,PO &b,PO &c)
{
    return (b.x-a.x)*(c.x-a.x)+(b.y-a.y)*(c.y-a.y);
}

inline bool segcross(LI &a,LI &b)
{
    int p1,p2,d1,d2;
    //b跨立a 
    p1=doublecmp(cross(a.a,a.b,b.a));
    p2=doublecmp(cross(a.a,a.b,b.b));
    //a跨立b 
    d1=doublecmp(cross(b.a,b.b,a.a));
    d2=doublecmp(cross(b.a,b.b,a.b));
    if(p1*p2<0&&d1*d2<0) return true;
    else return false;
}

inline void read()
{
    for(int i=1;i<=n;i++)
        scanf("%lf%lf%lf%lf",&li[i].a.x,&li[i].a.y,&li[i].b.x,&li[i].b.y);
}

inline void go()
{
    for(int i=1;i<=n;i++)
        for(int j=i+1;j<=n;j++)
            if(segcross(li[i],li[j])) {puts("burned!");return;}
    puts("ok!");
}

int main()
{
    while(scanf("%d",&n)!=EOF) read(),go();
    return 0;
}