hihocode_1227——ceil——The Cats' Feeding Spots

http://hihocoder.com/problemset/problem/1227

/************************************************
* Author        :Powatr
* Created Time  :2015/9/21 14:46:41
* File Name     :A.cpp
 ************************************************/

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int MAXN = 1e5 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-8;

double x[110], y[110];
double d[11000];
int main(){
    int T;
    scanf("%d", &T);
    while(T--){
        int n, m;
        scanf("%d%d", &n, &m);
        for(int i = 1; i <= n; i++)
            scanf("%lf%lf", &x[i], &y[i]);
        int ans = INF;
        for(int i = 1; i <= n; i++){
            int pos = 0;
                for(int j = 1; j <= n; j++){
                    d[++pos] = sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
                }
                sort(d + 1, d + pos + 1);
                int temp = ceil(d[m] + EPS);
                if(n == m){
                    ans = min(ans, temp);
                }
                else {
                    if(d[m+1] - temp > 0){
                        ans = min(ans, temp);
                    }
                }
        }
        if(ans == INF) puts("-1");
        else printf("%d\n", ans);
    }
    return 0;
}