NYOJ_83:迷宫寻宝（二）（计算几何）

#include<bits/stdc++.h>
using namespace std;

struct point
{
    double x,y;
    point operator -(const point& rhs)const
    {
        point ret;
        ret.x=x-rhs.x;
        ret.y=y-rhs.y;
        return ret;
    }
    double operator *(const point& rhs)const//叉乘
    {
        return x*rhs.y-y*rhs.x;
    }
    bool operator <(const point& rhs)const
    {
        return x<rhs.x||x==rhs.x&&y<rhs.y;
    }
} la[105],lb[105],en;
int n;

bool ok(point a,point b,point c,point d)
{
    return ((b-a)*(c-a))*((b-a)*(d-a))<0;
}

int cal(point A,point B)
{
    int ret=0;
    for(int i=0; i<n; i++)
        if(ok(la[i],lb[i],A,B))
            ret++;
    return ret;
}

int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        if(n<3)
        {
            puts("1");    //边界占一个
            continue;
        }
        for(int i=0; i<n; i++)
            scanf("%lf%lf%lf%lf",&la[i].x,&la[i].y,&lb[i].x,&lb[i].y);
        scanf("%lf%lf",&en.x,&en.y);
        int ans=1000;
        for(int i=0; i<n; i++)
        {
            ans=min(ans,cal(en,la[i]));
            ans=min(ans,cal(en,lb[i]));
        }
        printf("%d\n",ans+1);
    }
}