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input/code.cpp: In function 'int main()':
input/code.cpp:48:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   48 |     for (int i=0;i<nodes.size()-1;i++){
      |                  ~^~~~~~~~~~~~~~~

#include <iostream>
#include <vector>

using namespace std;

void visit(vector<vector<int>> & g, vector<int> & visited, int node, int component) {
    if (visited[node]) {
        return;
    } else {
        visited[node]=component;
        for (int next: g[node]){
            visit(g, visited, next, component);
        }
    }
}

int main(){

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

    vector<vector<int>> g(n+1, vector<int>(0));

    for (int i=0;i<m;i++){
        int v1, v2;
        cin >> v1 >> v2;

        g[v1].push_back(v2);
        g[v2].push_back(v1);



    }

    //cout << "A\n";
    int components=1;
    vector<int> visited(n+1, 0);
    vector<int> nodes(0);
    for (int node=1;node<=n;node++){
        if (visited[node]==0) {
            nodes.push_back(node);
            //cout << node << "\n";
            visit(g, visited, node, components);
            components++;
        }
    }
    cout << components-2 << '\n';
    for (int i=0;i<nodes.size()-1;i++){
        cout << nodes[i] << ' ' << nodes[i+1] << '\n';
    }


}

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