poj 3335 Rotating Scoreboard(半平面交)

刚开始学习半平面交，水个模板题，直接上模板

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <string>
#include <queue>
#include <algorithm>
#include <iostream>

using namespace std;

const double eps = 1e-6;

const int Max = 110;

typedef struct Point
{
    double x,y;

    Point() {}

    Point(double _x,double _y):x(_x),y(_y) {}

    Point operator + (const Point &a)const
    {
        return Point(x+a.x,y+a.y);
    }

    Point operator - (const Point &a)const
    {
        return Point(x-a.x,y-a.y);
    }

    double operator * (const Point &a)const
    {
        return x*a.x+y*a.y;
    }

    Point operator * (const double &a)const
    {
        return Point(x*a,y*a);
    }

    double operator ^ (const Point &a)const
    {
        return x*a.y-y*a.x;
    }
} Vector;

Point P[Max];

Point S[Max*10],T[Max*10];

int dbcmp(double a)
{
    return fabs(a)<eps?0:(a>0?1:-1);
}

int n;


Point GetLineIntersection(Point p,Vector v,Point q,Vector w)//计算两条直线的交点。
{
    Vector u = p-q;

    double t = (w^u)/(v^w);

    return p+v*t;
}


bool JudgePolygonNucleus()
{
    int  num1 = n;

    int num2;

    for(int i = 0; i<n; i++) //初始的多边形的核为他自己本身
    {
        S[i] = P[i];
    }

    for(int i = 0; i<n; i++)
    {


        num2= 0 ;

        for(int j = 0; j<num1; j++)
        {
            int ans1 = dbcmp((P[(i+1)%n]-P[i])^(S[j]-P[i]));

            int ans2 = dbcmp((P[(i+1)%n]-P[i])^(S[(j+1)%num1]-P[i]));


            if(ans1<=0)//通过叉积判断是不是在直线的某一侧
            {
                T[num2++] = S[j];
            }

            if(ans1*ans2<0)
            {
                T[num2++] = GetLineIntersection(P[i],P[(i+1)%n]-P[i],S[j],S[(j+1)%num1]-S[j]);
            }
        }
        num1 = num2;


        for(int j = 0; j<num2; j++)
        {
            S[j] = T[j];
        }

    }

    return num1!=0;

}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(int i = 0; i<n; i++)
            scanf("%lf %lf",&P[i].x,&P[i].y);
        if(JudgePolygonNucleus())
            printf("YES\n");
        else
            printf("NO\n");

    }
    return 0;
}