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input/code.cpp: In member function 'void compute::assign(int)':
input/code.cpp:43:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |         for (int j=0;j<data[i].size();j++) {
      |                      ~^~~~~~~~~~~~~~~

#include <iostream>
#include <vector>

using std::cout;
using std::endl;
#define DEBUG std::cout<<"LINE"<<__LINE__
#define IN(A) int A;std::cin>>A;

struct compute {
    std::vector<std::vector<int>> data;
    std::vector<std::pair<int,int>> result;
    std::vector<bool> visited;
    bool start() {

        IN(n);
        IN(m);
        data.assign(n,{});
        visited.assign(n,false);
        for (int i=0;i<m;i++) {
            IN(a);
            IN(b);
            a=a-1;
            b=b-1;
            data[a].emplace_back(b);
            data[b].emplace_back(a);
        }
        assign(0);
        for (int i=0;i<n;i++) {
            if (!visited[i]) {
                result.emplace_back(1,i+1);
                assign(i);
            }
        }
        cout<<result.size()<<endl;
        for (auto res:result) {
          cout<<res.first<<" "<<res.second<<endl;
        }
        return true;
    }
    void assign(int i) {
        if (visited[i]) return;
        visited[i]=true;
        for (int j=0;j<data[i].size();j++) {
            assign(data[i][j]);
        }
    }
};

int main() {
    compute comp;
    comp.start();


}

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