Connect cities

#include <iostream>
#include <vector>
using namespace std;

#define MAX_N (int)1e5
int n, m;
vector<int> adj[MAX_N];
vector<int> bridges;
bool visited[MAX_N] = {false};


void dfs(int s) {
		if(visited[s]) return;
		visited[s] = true;
		int len = adj[s].size();
		for(int i = 0; i < len; ++i){
			dfs(adj[s][i]);
		}
}

int main(){
	cin >> n >> m;
	for(int i = 0; i < m; i++){
		int a, b;
		cin >> a >> b;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	
	for(int i = 1; i <= n; i++){
		if(!visited[i]) {
			bridges.push_back(i);
			dfs(i);
		}
	}
	int s = bridges.size() - 1;
	cout << s << endl;
	for(int i = 0; i < s; i++){
		cout << bridges[i] << " " << bridges[i + 1] << endl;
	}
	
	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: RUNTIME ERROR

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

Test 7

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

Test 8

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

Test 9

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

Test 10

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: ACCEPTED