Connect cities

input/code.cpp: In function 'int get_new_city(bool*, size_t)':
input/code.cpp:8:12: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' {aka 'long unsigned int'} [-Wsign-compare]
    8 |   for (; i < size; i++) {
      |          ~~^~~~~~

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

int get_new_city(bool *visited, size_t size) {
  static int i = 1;
  for (; i < size; i++) {
    if (!visited[i])
      return i;
  }
  return -1;
}

void dfs(int c, bool *v, vector<int> *adj) {
  if (v[c])
    return;
  v[c] = true;

  for (auto nc : adj[c]) {
    dfs(nc, v, adj);
  }
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);

  int n, m;
  cin >> n >> m;

  bool visited[n + 1];
  memset(visited, 0, (n + 1) * sizeof(bool));

  vector<int> adj[n + 1];
  int f, s;
  for (int i = 0; i < m; i++) {
    cin >> f >> s;
    adj[f].push_back(s);
    adj[s].push_back(f);
  }

  vector<pair<int, int>> new_roads;
  int p_city = 0, c_city;
  while ((c_city = get_new_city(visited, n + 1)) != -1) {
    if (p_city != 0) {
      new_roads.push_back(make_pair(p_city, c_city));
    }
    p_city = c_city;
    dfs(c_city, visited, adj);
  }

  cout << new_roads.size() << "\n";
  for (auto p : new_roads) {
    cout << p.first << " " << p.second << "\n";
  }

  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