POJ 2653 Pick-up sticks

蒻苣：弱弱很弱，路过的巨巨还不吝赐教！^.^...QAQ

题意：给你n个线段，求最上面的线段有多少个（没有被后面添加的线段相交）

题解：直接暴力即可。对于当前第i个线段，枚举i+1~n-1 是否有线段与其相加 有的话这条线段就是被覆盖的，也就是不要输出的

代码：

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <cmath>
using namespace std;
const double INF  = 1E200;
const double wc = 1E-8;
struct POINT{
        double x,y;
        POINT( double a = 0,double b = 0 )  { x = a; y = b; }
};
struct LINESEG{
        POINT e;
        POINT s;
        LINESEG( POINT x,POINT y ) { e = x; s = y; }
        LINESEG(){}
};
LINESEG L[100000+10];
double dist(POINT p1,POINT p2)              
{
 return( sqrt( (p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y) ) );
}
double multiply(POINT sp,POINT ep,POINT op)
{
 return((sp.x-op.x)*(ep.y-op.y)-(ep.x-op.x)*(sp.y-op.y));
}
bool online(LINESEG l,POINT p)
{
 return( (multiply(l.e,p,l.s)==0) &&( ( (p.x-l.s.x)*(p.x-l.e.x)<=0 )&&( (p.y-l.s.y)*(p.y-l.e.y)<=0 ) ) );
}
bool intersect(LINESEG u,LINESEG v)
{
 return( (max(u.s.x,u.e.x)>=min(v.s.x,v.e.x))&&                     
   (max(v.s.x,v.e.x)>=min(u.s.x,u.e.x))&&
   (max(u.s.y,u.e.y)>=min(v.s.y,v.e.y))&&
   (max(v.s.y,v.e.y)>=min(u.s.y,u.e.y))&&
   (multiply(v.s,u.e,u.s)*multiply(u.e,v.e,u.s)>=wc)&&         
   (multiply(u.s,v.e,v.s)*multiply(v.e,u.e,v.s)>=wc));
}
bool intersect_A(LINESEG u,LINESEG v)
{
 return ((intersect(u,v))&&
   (!online(u,v.s))&&
   (!online(u,v.e))&&
   (!online(v,u.e))&&
   (!online(v,u.s)));
}
bool intersect_l(LINESEG u,LINESEG v)
{
 return multiply(u.s,v.e,v.s)*multiply(v.e,u.e,v.s)>=wc;
}
int vis[100000+50];
int main()
{
        int n;
        while(cin>>n)
        {
                if(!n) break;
                memset(vis,0,sizeof(vis));
                for(int i = 0;i < n; i++)
                        scanf("%lf%lf%lf%lf",&L[i].e.x,&L[i].e.y,&L[i].s.x,&L[i].s.y);
                for(int i = 0;i < n; i++)
                        for(int j = i+1;j < n; j++)
                                if(intersect_A(L[i],L[j]))
                                        {vis[i]=1;break;}
                int flag = 0;
                printf("Top sticks:");
                for(int i = 0;i < n;i++)
                {
                        if(vis[i]==0){
                                if(flag==0)
                                {printf(" %d",i+1);flag=1;}
                                else
                                printf(", %d",i+1);
                        }
                }
                puts(".");
        }
}