并查集+按秩合并

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

const int N = 5e5+50;

int n,lst;
struct UnionTable
{
    int f[N],s[N],v[N],d[N];
    void init(int n)
    {
        for(int i=1; i<=n; i++) f[i]=i,v[i]=0,s[i]=1;
    }
    int find(int x)
    {
        if(f[x]^x)
        {
            int fa=find(f[x]);
            d[x]=d[f[x]]+1;
            return fa;
        }
        else return x;
    }
    void Union(int x,int y,int c)
    {
        int f1=find(x),f2=find(y);
        if(f1==f2) return;
        if(s[f1]>s[f2]) f[f2]=f1,v[f2]=c,s[f1]+=s[f2];
        else f[f1]=f2,v[f1]=c,s[f2]+=s[f1];
    }
    int Query(int x,int y)
    {
        int f1=find(x),f2=find(y),r=0;
        if(f1!=f2) return -1;
        while (x!=y)
        {
            if(d[x]<d[y]) swap(x,y);
            r=max(r,v[x]),x=f[x];
        }
        return r;
    }
} un;

int main()
{
    int T,m;
    scanf ("%d",&T);
    while (T--)
    {
        scanf ("%d%d",&n,&m);
        un.init(n);
        int c=0;
        while (m--)
        {
            int op,u,v;
            scanf ("%d%d%d",&op,&u,&v);
            if(op==1) un.Union(u,v,++c);
            else {printf("%d\n",un.Query(u,v));++c;}
        }
    }
    return 0;
}