poj 1696 Space Ant

#include<stdio.h>
#include<algorithm>
using namespace std;
const int Max=55;
struct Point
{
int x,y,num;
} p[Max],res[Max];
int pos;
int xmult(Point p1,Point p2,Point p0)
{
return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}
int dis(Point p1,Point p2)
{
return (p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y);
}
bool cmp(Point p1,Point p2)
{
int tmp=xmult(p1,p2,p[pos]);
if(tmp>0)
return true;
if(!tmp&&dis(p[pos],p1)<dis(p[pos],p2))
return true;
return false;
}
int main()
{
int _case,n,i;
scanf("%d",&_case);
while(_case--)
{
scanf("%d",&n);
for(i=0;i<n;i++)
{
scanf("%d%d%d",&p[i].num,&p[i].x,&p[i].y);
if(p[i].y<p[0].y||p[i].y==p[0].y&&p[i].x<p[0].x)
swap(p[i],p[0]);
}
for(i=1;i<n;i++)
{
pos=i-1;
sort(p+i,p+n,cmp);
}
printf("%d ",n);
for(i=0;i<n-1;i++)
printf("%d ",p[i].num);
printf("%d\n",p[n-1].num);
}
}