POJ 2653

开一个数组做成队列来搜索就好了。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;

const int MAXN=100010;

typedef struct po{
    double x,y;
}Point;
struct e{
    Point start,end;
}edge[MAXN],ss,ee;
int n;
double x1,y1,x2,y2;
Point start,end;
int que[MAXN*100];

double multi(Point p1, Point p2, Point p0){
    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}

bool slove(int k,int i){
    ss=edge[k]; ee=edge[i];
    if(max(ss.start.x,ss.end.x)>=min(ee.start.x,ee.end.x)&&
       max(ee.start.x,ee.end.x)>=min(ss.start.x,ss.end.x)&&
       max(ss.start.y,ss.end.y)>=min(ee.start.y,ee.end.y)&&
       multi(ee.start,ss.end,ss.start)*multi(ss.end,ee.end,ss.start)>0&&
       multi(ss.start,ee.end,ee.start)*multi(ee.end,ss.end,ee.start)>0){
           return true;
       }
     return false;           
}

int main(){
    int f,l;
    while(scanf("%d",&n)!=EOF){
        if(n==0) break; f=l=0;
        for(int i=1;i<=n;i++){
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
            start.x=x1; start.y=y1;
            end.x=x2; end.y=y2;
            edge[i].start=start; edge[i].end=end;
            if(i>1){
                int size=l-f;
                while(size--){
                    int k=que[f++];
                    if(!slove(k,i))
                    que[l++]=k;
                }
            }
            que[l++]=i;
        }
        bool flag=false;
        printf("Top sticks:");
        while(f<l){
            int i=que[f++];
            if(!flag){
                     printf(" %d",i);
                     flag=true;
            }
            else{
                    printf(", %d",i);
            }
        }
        printf(".
");
    }
    return 0;
}