ZOJ 10th Anniversary Contest - I A Song of Anniversary

#include<stdio.h>
#include<math.h>
#include<vector>
#include<algorithm>
using namespace std;
inline double sqr(double x)
{
    return x*x;
}
struct Point
{
    int x,y;
    int time;
    bool operator < (const Point & p2) const
    {
        return time<p2.time;
    }
    double operator ^ (const Point & p2) const
    {
        return sqrt(sqr(x-p2.x)+sqr(y-p2.y));
    }
    void read(const char * s)
    {
        sscanf(s,"%d,%d,%d,%*d,%*d",&x,&y,&time);
    }
};
vector <Point> vp;
int k;
bool read()
{
    static bool first=true;
    if (first)
    {
        if (scanf("%*s")==EOF) return false;
        first=false;
    }
    if (scanf("%d",&k)==EOF) return false;
    vp.clear();
    static char s[256];
    while (1)
    {
        if (scanf("%s",s)==EOF) return true;
        if (s[0]=='[') return true;
        Point p;
        p.read(s);
        vp.push_back(p);
    }
    return true;
}
vector<double> vd;
int main()
{
    freopen("i.in","r",stdin);
    while (read())
    {
        sort(vp.begin(),vp.end());
        vd.clear();
        int n=vp.size();
        int i;
        for (i=1;i<n;i++)
        {
            vd.push_back(vp[i]^vp[i-1]);
        }
        sort(vd.begin(),vd.end());
        double ans;
        if (k==0) ans=0; else ans=vd[n-k];
        printf("%.3f\n",ans);
    }
    return 0;
}