Connect cities

input/code.cpp: In function 'void connect_cities()':
input/code.cpp:46:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |     for (int i = 0; i < components.size() - 1; i++) {
      |                     ~~^~~~~~~~~~~~~~~~~~~~~~~

#include <bits/stdc++.h>


// book copy-pasta
const int N = 10e5;
std::vector<int> adj[N];
bool visited[N];

void dfs(int s) {
    if (visited[s]) return;
    visited[s] = true;
    for (auto u: adj[s]) {
        dfs(u);
    }
}

void connect_cities() {
    int n, m;
    std::cin >> n >> m;

    for (int i = 1; i <= n; i++) visited[i] = false;

    for (int i = 0; i < m; i++) {
        int s, t;
        std::cin >> s >> t;
        adj[s].push_back(t);
        adj[t].push_back(s);
    }

    // disjoint components (one element from each disjoint component)
    std::vector<int> components;

    for (int i = 1; i <= n; i++) {
        if (!visited[i]) {
            // found an unvisited node, add that to components
            components.push_back(i);
            // then mark all adjacent nodes as visited
            dfs(i);
        }
    }

    // we need as many rodes as there are disjoint components minus one
    std::cout << components.size() - 1 << std::endl;

    // add a road between elements in pairs of disjoint components
    for (int i = 0; i < components.size() - 1; i++) {
        std::cout << components[i] << " " << components[i + 1] << std::endl;
    }
}

int main() {
    std::basic_ostream<char, std::char_traits<char>>::sync_with_stdio(false);
    std::cin.exceptions(std::istream::failbit);

    connect_cities();

    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