Connect cities

input/code.cpp: In function 'int main()':
input/code.cpp:36:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   36 |     for(int i=1;i<cont.size();i++)
      |                 ~^~~~~~~~~~~~

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
vector<long long> adj[N];
bool visited[N];
void dfs(long long u)
{
    visited[u]=true;
    for(long long v:adj[u])
    {
        if(visited[v]==0)dfs(v);
    }
}
int main()
{
    long long n,m;
    cin>>n>>m;
    for(int i=0;i<m;i++)
    {
        long long a,b;
        cin>>a>>b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    vector<long long> cont;
    for(int i=1;i<=n;i++)
    {
        if(visited[i]==0)
        {
            cont.push_back(i);
            dfs(i);
        }

    }
    cout<<cont.size()-1<<endl;
    for(int i=1;i<cont.size();i++)
    {
        cout<<cont[i-1]<<" "<<cont[i]<<endl;
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED