信友队T4 10pts 求调

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
int T,n,m,i,x,y,ans;
vector<int> G[N];
bool vis[N];
int p[N];
void dfs(int x)
{
    vis[x]=true;
    for (int to:G[x])
    {
        if (!vis[to]) dfs(to);
    }
}
void work()
{
    ans=0;
    scanf("%d%d",&n,&m);
    for (i=1;i<=n;i++) G[i].clear();
    for (i=1;i<=m;i++)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for (i=1;i<=n;i++) vis[i]=false;
    for (i=1;i<=n;i++)
    {
        if (!vis[i]) 
        {
            p[++ans]=i;
            dfs(i);
        }
    }
    printf("%d\n",ans-1);
    for (i=1;i<=ans-1;i++) printf("%d %d\n",p[i],p[i+1]);
}
int main()
{
    freopen("destiny.in","r",stdin);
    freopen("destiny.out","w",stdout); 
    scanf("%d",&T);
    while (T--) work();
    return 0;
}