Connect cities

#include <bits/stdc++.h>
#define fast ios::sync_with_stdio(0); cin.tie(0);
#define fill(arr,val) memset(arr,val,sizeof(arr))
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define ll long long
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define ii pair<int,int>
#define iii pair<int,pair<int,int>>
#define dq deque<int>
#define nend '\n'
using namespace std;

const ll inf=1e18;
const int dx[]={1,0,-1,0};
const int dy[]={0,1,0,-1};
const int N=2e5+4;
int n,m,a[N],par[N];
ii edge[N];
int tplt;
int aces(int x) {
    if (x!=par[x]) return par[x]=aces(par[x]);
    else return x;
}
void join(int x, int y) {
    int u=aces(x), v=aces(y);
    if (u!=v) {
        par[u]=v;
        tplt--;
    }
}
vector<ii>ans;
int main() {
    //freopen("file.inp","r",stdin);
    //freopen("file.out","w",stdout);
    fast;
    cin >> n >> m;
    tplt=n;
    for (int i=1; i<=n; i++) {
        par[i]=i;
    }
    for (int i=1; i<=m; i++) {
        cin >> edge[i].fi >> edge[i].se;
        join(edge[i].fi,edge[i].se);
    }
    for (int i=1; i<n; i++) {
        if (aces(i)!=aces(i+1) and tplt>1) {
            join(i,i+1);
            ans.pb({i,i+1});
        }
    }
    cout << ans.size() << nend;
    for (auto d:ans) {
        cout << d.fi << ' ' << d.se << nend;
    }






    return 0;
}

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