POJ2653——Pick-up sticks

题目链接：http://poj.org/problem?id=2653

Pick-up sticks

题目大意：给你n条线段，依次放入平面直角坐标系中，先放的，如果与后面放的线段相交，则被压住，最后要你统计没被压住的线段的个数。

直接套线段相交的模板即可！！！

#include<iostream>#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>using namespace std;const double eps=1e-10;struct point{    double x,y;}p[100010],q[100010];int vis[100010];bool inter(point a,point b,point c,point d){    if(min(a.x,b.x)>max(c.x,d.x)||min(a.y,b.y)>max(c.y,d.y)||min(c.x,d.x)>max(a.x,b.x)||min(c.y,d.y)>max(a.y,b.y))        return 0;    double h,i,j,k;    h=(b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);    i=(b.x-a.x)*(d.y-a.y)-(b.y-a.y)*(d.x-a.x);    j=(d.x-c.x)*(a.y-c.y)-(d.y-c.y)*(a.x-c.x);    k=(d.x-c.x)*(b.y-c.y)-(d.y-c.y)*(b.x-c.x);    return h*i<=eps&&j*k<=eps;}int main(){    int n;    while(scanf("%d",&n),n)    {        int i,j;        memset(vis,0,sizeof(vis));        for(i=1;i<=n;i++)            scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&q[i].x,&q[i].y);        for(i=1;i<=n;i++)            for(j=i+1;j<=n;j++)            {                if(inter(p[i],q[i],p[j],q[j]))                {                    vis[i]=1;                    break;                }            }        printf("Top sticks:");        for(i=1;i<=n;i++)            if(!vis[i])            {                printf(" %d",i);                break;            }        for(i++;i<=n;i++)            if(!vis[i])                printf(", %d",i);        printf(".\n");    }    return 0;}