https://ac.nowcoder.com/acm/contest/view-submission?submissionId=41630926
一条1到n按顺序链接的链即可卡成
而这个代码是可以过纯随机数据的。
数据生成器：

#include<bits/stdc++.h>
#define maxn 300005
using namespace std;

int Ran(){ return rand() << 15 | rand(); }
int Ran(int a,int b){ return Ran() % (b-a+1) + a; }
int F[maxn];
int Find(int u){ return !F[u] ? u : F[u] = Find(F[u]); }

int main(){
    srand(time(NULL));
    freopen("3.in","w",stdout);
    int n = 300000 , m = 300000;
    printf("%d %d\n",n,m);
    for(int i=1;i<n;i++){
        int u = i , v = i+1;
        for(;Find(u) == Find(v);u=Ran(1,n),v=Ran(1,n));
        printf("%d %d %d\n",u,v,Ran(1,10000000));
        F[Find(u)] = Find(v);
    }
    for(;m--;){
        printf("%d %d\n",1,Ran(1,n));
    }
}