Max Angle HDU - 3532

又回到极角排序，其实自己真的没有搞懂这个东西但是知道怎么用

#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdio>

using namespace std;

const int maxn=1111;
const double eps=1e-8;
const double PI=acos(-1.0);

int sgn(double x)
{
    if(fabs(x)<eps)
        return 0;
    if(x<0)
        return -1;
    else
        return 1;
}
struct Point
{
    double x,y;
    Point(){}
    Point(double _x,double _y)
    {
        x=_x;
        y=_y;
    }
    Point operator -(const Point &b)const
    {
        return Point(x-b.x,y-b.y);
    }
    double operator ^(const Point &b)const
    {
        return x*b.y-y*b.x;
    }
    double operator *(const Point &b)const
    {
        return x*b.x+y*b.y;
    }
};

int i;
Point p[maxn];

double dist(Point a,Point b)
{
    return sqrt((a-b)*(a-b));
}
bool cmp(Point a,Point b)
{
    int ans=sgn((a-p[0])^(b-p[0]));
    if(ans==1)
        return true;
    else if(ans==0)
        return dist(a,p[0])<dist(b,p[0]);
    else
        return false;
}
double num[maxn];
double num1[maxn];
bool cmp1(double a,double b)
{
    return a>b;
}
int main()
{
    int n;
    while(1)
    {
        cin>>n;
        if(n==-1)
            break;
        for(int i=0;i<n;i++)
        {
            cin>>p[i].x>>p[i].y;
        }
        int cont=0;
        int cont1=0;
        sort(p+1,p+n,cmp);
        for(int j=2;j<n;j++)
        {
            num[cont++]=acos(((p[j]-p[0])*(p[j-1]-p[0]))/(dist(p[0],p[j])*dist(p[0],p[j-1])))*180.0/PI;
        }
        sort(num,num+cont);
        num1[cont1++]=num[0];
        for(i=1;i<n;i++)
        {
            swap(p[0],p[i]);
            sort(p+1,p+n,cmp);
            cont=0;
            for(int j=2;j<n;j++)
            {
                num[cont++]=acos(((p[j]-p[0])*(p[j-1]-p[0]))/(dist(p[0],p[j])*dist(p[0],p[j-1])))*180.0/PI;
            }
            sort(num,num+cont);
            num1[cont1++]=num[0];
        }
        sort(num1,num1+cont1,cmp1);
        printf("%.4lf\n",num1[0]);
    }
    return 0;
}