POJ 2653 Pick-up sticks

#include<cstdio>
#include<cstring>
#include<vector>
#include<cmath>
#include<queue>
#include<list>
#include<algorithm>
using namespace std;

const int maxn=100000+10;
const double eps=1e-8;
int totP,totL;
struct point
{
    double x;
    double y;
} p[2*maxn];
struct Line
{
    point a;
    point b;
    int id;
} line[maxn];
vector<Line> v;
vector <Line>::iterator Iter;
vector<int> ans;

int flag[maxn];

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

int opposite_side(point p1,point p2,point l1,point l2)
{
    return xmult(l1,p1,l2)*xmult(l1,p2,l2)<-eps;
}

int intersect_ex(point u1,point u2,point v1,point v2)
{
    return opposite_side(u1,u2,v1,v2)&&opposite_side(v1,v2,u1,u2);
}

int main()
{
    while(~scanf("%d",&totL))
    {
        if(!totL) break;
        totP=0;
        for(int i=0; i<totL; i++)
        {
            double a,b,c,d;
            scanf("%lf%lf%lf%lf",&a,&b,&c,&d);
            p[totP+0].x=a;
            p[totP+0].y=b;
            p[totP+1].x=c;
            p[totP+1].y=d;

            line[i].a=p[totP+0];
            line[i].b=p[totP+1];
            line[i].id=i;
            totP=totP+2;
        }
        v.clear();
        for(int i=0; i<totL; i++)
        {
            for (Iter=v.begin();Iter!=v.end();)
            {
                Line now=*Iter;
                if(intersect_ex(line[i].a,line[i].b,now.a,now.b))
                    Iter = v.erase(Iter);
                else Iter++;
            }
            v.push_back(line[i]);
        }

        ans.clear();
        for (Iter=v.begin();Iter!=v.end();Iter++ )
        {
            Line now=*Iter;
            ans.push_back(now.id);
        }
        printf("Top sticks: ");
        for(int i=0; i<ans.size(); i++)
        {
            printf("%d",ans[i]+1);
            if(i<ans.size()-1) printf(", ");
            else printf(".\n");
        }
    }
    return 0;
}