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;

}