poj 2653 Pick-up sticks(判断线段相交)

题意：扔了n个棍子，如果某些棍子上边没有被别的棍子压住，则输出这些棍子，按照输入的顺序输出
思路：暴力枚举
做的时候忘了判断 共线但不相交的情况了，wa了好几发

#include <iostream>#include <cmath>#include <cstdio>#include <algorithm>#include <queue>#include <cstring>using namespace std;struct Point{    double x,y;};struct Line{    Point sp,ep;};const double precision = 1e-8;const int MAXN = 100010;int n;Line ls[MAXN];int dblcmp(double d){    if(fabs(d) < precision)        return 0;    return d > 0 ? 1:-1;}double det(Point a, Point b, Point c){    //b.x-a.x,b.y-a.y    //c.x-a.x,c.y-a.y    return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);}int xyCmp(double p, double mini, double maxi){    return dblcmp(p-mini)*dblcmp(p-maxi);}int betweenCmp(Point a, Point b, Point c){    if(fabs(b.x-c.x) > fabs(b.y-c.y))        return xyCmp(a.x,min(b.x,c.x),max(b.x,c.x));    else        return xyCmp(a.y,min(b.y,c.y),max(b.y,c.y));}bool intersect(int i, int j){    //判断是否相交（不包括顶点重合）    int d1 = dblcmp(det(ls[i].sp,ls[i].ep,ls[j].sp));    int d2 = dblcmp(det(ls[i].sp,ls[i].ep,ls[j].ep));    int d3 = dblcmp(det(ls[j].sp,ls[j].ep,ls[i].sp));    int d4 = dblcmp(det(ls[j].sp,ls[j].ep,ls[i].ep));    if(d1*d2 < 0 && d3*d4 < 0)        return true;    //判断顶点重合的情况  和  共线但不相交的情况    if(d1 == 0 && betweenCmp(ls[j].sp,ls[i].sp,ls[i].ep) <= 0 ||       d2 == 0 && betweenCmp(ls[j].ep,ls[i].sp,ls[i].ep) <= 0 ||       d3 == 0 && betweenCmp(ls[i].sp,ls[j].sp,ls[j].ep) <= 0 ||       d4 == 0 && betweenCmp(ls[i].ep,ls[j].sp,ls[j].ep) <= 0)        return true;    return false;}int main(){    //freopen("in","r",stdin);    bool flag;    while(scanf("%d",&n) && n)    {        for(int i = 1; i <= n; ++i)            scanf("%lf %lf %lf %lf",&ls[i].sp.x,&ls[i].sp.y,&ls[i].ep.x,&ls[i].ep.y);        queue<int> que;        for(int i = 1; i <= n; ++i)        {            flag = true;            for(int j = i+1; j <= n; ++j)            {                if(intersect(i,j))                {                    flag = false;                    break;                }            }            if(flag)                que.push(i);        }        printf("Top sticks:");        while(que.size() > 1)        {            printf(" %d,",que.front());            que.pop();        }        printf(" %d.\n",que.front());        que.pop();    }    return 0;}