注意输出格式
#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>
using namespace std;
const int N = (55 * 99 + 10)*2;
int p[N];
struct Line
{int s, e;double len;
}q[N];
double x[N], y[N];
double dis(double x1, double y1, double x2, double y2)
{return sqrt((x1-x2)*(x1-x2) + (y1-y2)*(y1-y2));
}
int cmp(Line a, Line b)
{return a.len < b.len;
}
int find(int x)
{return x == p[x]? x:find(p[x]);
}
int main(void)
{int kase;scanf("%d", &kase);while(kase--){int n, sum = 0;scanf("%d", &n);for(int i = 0;i < n;i++){scanf("%lf %lf", &x[i], &y[i]);for(int j = 0;j < i;j++){double len = dis(x[i], y[i], x[j], y[j]);q[sum++] = {i, j, len};}}sort(q, q+sum, cmp);for(int i = 0;i <= sum;i++)p[i] = i;double ans = 0.0;for(int i = 0;i < sum;i++){int fa = find(q[i].s);int fb = find(q[i].e);if(fa != fb){p[fa] = fb;ans += q[i].len;}}printf("%.2lf\n", ans);if(kase != 0)printf("\n");}return 0;
}