Connect the Graph mk2

#include<stdio.h>
#include<vector>
#include<stack>
using namespace std;

int n,m;
vector<int> adj[100010];
bool visited[100010];

void dfs(int uc)
{
    stack<int> st;
    st.push(uc);

    while(!st.empty()){
        int u = st.top();
        st.pop();
        if(visited[u])continue;
        visited[u] = true;

        for(int i=0;i<adj[u].size();i++){
            int v = adj[u][i];
            if(!visited[v]){
                st.push(v);
            }
        }
    }
}

int main()
{
    scanf("%d %d",&n,&m);
    for(int i=0;i<m;i++){
        int u,v;
        scanf("%d %d",&u,&v);
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    int prev = -1;
    vector<pair<int,int> > ans;
    for(int i=1;i<=n;i++){
        if(!visited[i]){
            dfs(i);
            if(prev != -1){
                ans.push_back({prev,i});
            }
            prev = i;
        }
    }
    printf("%d\n",ans.size());
    for(int i=0;i<ans.size();i++){
        printf("%d %d\n",ans[i].first,ans[i].second);
    }
    return 0;
}