pku 1696[计算几何]

pku 1696[计算几何]

#include < stdio.h >
#include < math.h >
#include < memory.h >
// using namespace std;
#define  eps 1e-8
#define  MAXN 50
#define  PI 3.1415926535898
struct  point { double x,y;} ;

point planet[MAXN + 1 ];
bool  visit[MAXN + 1 ];
int  ans[MAXN + 1 ];

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

double  distance(point p1,point p2) {
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}

int  main()
{
    int t,indice,i,j,k,n;
    double max;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(i=1;i<=n;i++)
            scanf("%d%lf%lf",&indice,&(planet[i].x),&(planet[i].y));

        memset(visit,0,sizeof(visit));

        int next=1;

        for(i=2;i<=n;i++)
            if(planet[next].y>planet[i].y)
                next=i;
            else if(planet[next].y == planet[i].y)
                if(planet[next].x>planet[i].x)
                    next=i;
        point p1,p0;
        p1.x=0;
        p1.y=planet[next].y;
        p0.x=planet[next].x;
        p0.y=planet[next].y;
        k=0;
        double thta,max;
        for(j=1;j<=n;j++)
        {
            visit[next]=true;
            ans[k++]=next;
            max=2*PI;
            for(i=1;i<=n ; i++)
            {
                if(visit[i]) continue;    
                double xmul=xmult(p0,p1,planet[i]);
                double dmul=dmult(p0,p1,planet[i]);
                if( xmul<=0)
                {
                    if(dmul==0 )
                        thta=3*PI/2.0;
                    else 
                        if(dmul<0 ) thta=PI+atan(xmul/dmul);
                        else  thta=2*PI+atan(xmul/dmul);

                }
                if( thta<max || 
                    (fabs(thta-max)<eps && fabs(distance(p0,planet[i])-distance(p0,planet[next]))<eps)
                    )
                { next=i;max=thta;}
            }
            p1.x=p0.x;
            p1.y=p0.y;
            p0.x=planet[next].x;
            p0.y=planet[next].y;
        }
        printf("%d",k);
        for(i=0;i<k;i++)
            printf(" %d",ans[i]);
        printf("\n");
    }
    return 0;
}