poj 2653 （线段相交判断）

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <iostream>
#include <stdlib.h>
#include <math.h>
#include <algorithm>

using namespace std;
#define MAXX 100010
#define eps 1e-6

typedef struct point
{
    double x,y;
}point;

typedef struct
{
    point st,ed;
}line;

bool  xy(double x,double y){ return x<y-eps; }
bool  dy(double x,double y){ return x>y+eps; }
bool xyd(double x,double y){ return x<y+eps; }
bool dyd(double x,double y){ return x>y-eps; }
bool  dd(double x,double y){ return fabs(x-y)<eps; }

double crossProduct(point a,point b,point c)
{
    return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
}

bool onSegment(point a,point b,point c)
{
    double maxx=max(a.x,b.x);
    double maxy=max(a.y,b.y);
    double minx=min(a.x,b.x);
    double miny=min(a.y,b.y);
    if(dd(crossProduct(a,b,c),0.0)&&dyd(c.x,minx)
           &&xyd(c.x,maxx)&&dyd(c.y,miny)&&xyd(c.y,maxy))
        return true;
    return false;
}

bool segIntersect(point p1,point p2,point p3,point p4)
{
    double d1=crossProduct(p3,p4,p1);
    double d2=crossProduct(p3,p4,p2);
    double d3=crossProduct(p1,p2,p3);
    double d4=crossProduct(p1,p2,p4);
    if(xy(d1*d2,0.0)&&xy(d3*d4,0.0))
        return true;
    if(dd(d1,0.0)&&onSegment(p3,p4,p1))
        return true;
    if(dd(d2,0.0)&&onSegment(p3,p4,p2))
        return true;
    if(dd(d3,0.0)&&onSegment(p1,p2,p3))
        return true;
    if(dd(d4,0.0)&&onSegment(p1,p2,p4))
        return true;
    return false;
}

point p[MAXX];
line li[MAXX];
int num[MAXX];

int main()
{
    int m,n,i,j;
    while(scanf("%d",&n)!=EOF&&n)
    {
        memset(num,0,sizeof(num));
        for(i=0;i<n;i++)
        {
            scanf("%lf%lf%lf%lf",&li[i].st.x,&li[i].st.y,&li[i].ed.x,&li[i].ed.y);
        }
        for(i=0;i<n;i++)
        {
            for(j=i+1;j<n;j++)
            {
                if(segIntersect(li[i].st,li[i].ed,li[j].st,li[j].ed))
                {
                    num[i]++;
                    break;
                }

            }
        }
        int cas=0,tes=0,tmp;
        //int str[MAXX];
        for(i=0;i<n;i++)
        {
            if(num[i] == 0)
            {
                cas++;
            }
        }
        printf("Top sticks: ");
        for(i=0;i<n;i++)
        {
            if(num[i] == 0 && tes<cas-1)
            {
                printf("%d, ",i+1);
                tes++;
                tmp=i;
            }
        }//printf("%d**",i);
        for(j=tmp+1;j<n;j++)
        {
            if(num[j] == 0)
            {
                printf("%d.\n",j+1);
            }
        }
    }
    return 0;
}