@[Claire0918](/user/660816) 首先你并查集函数就写错了。
by Adchory @ 2022-12-30 19:26:26
```cpp
#include<bits/stdc++.h>
using namespace std;
const int maxn = 500 + 10;
struct pos{
int x, y;
};
struct edge{
int p1, p2, d;
};
bool cmp(const edge & a, const edge & b){
return a.d < b.d;
}
int s, p;
pos a[maxn];
int father[maxn];
int c;
double res = -1;
vector<edge> G;
inline int get_father(int x){
if (father[x] == x){
return x;
}
father[x] = get_father(father[x]);
return father[x];
}
int main(){
scanf("%d %d", &s, &p);
for (int i = 1; i <= p; i++){
father[i] = i;
}
for (int i = 1; i <= p; i++){
scanf("%d %d", &a[i].x, &a[i].y);
for (int j = 1; j < i; j++){
G.push_back({i, j, (a[i].x - a[j].x) * (a[i].x - a[j].x) + (a[i].y - a[j].y) * (a[i].y - a[j].y)});
}
}
sort(G.begin(), G.end(), cmp);
c = p;
for (auto x: G){
int ti = get_father(x.p1), tj = get_father(x.p2);
if (ti != tj){
father[ti] = tj;
c--;
res = max(res, sqrt(x.d));
}
if (c == s){
break;
}
}
printf("%.2lf", res);
return 0;
}
```
@[Reimu_Hakurei](/user/590600)
by Claire0918 @ 2022-12-30 19:36:43
[评测记录](https://www.luogu.com.cn/record/98289866)
过了，谢谢。
by Claire0918 @ 2022-12-30 19:39:02
@[Reimu_Hakurei](/user/590600) 但是并查集哪里错了
by Claire0918 @ 2022-12-30 19:43:02
@[Claire0918](/user/660816) `father[x] == get_father(father[x]);` 看清楚点……
by Adchory @ 2022-12-30 19:44:09
啊这……
by Claire0918 @ 2022-12-30 19:46:47