Sukat

input/code.cpp: In function 'int main()':
input/code.cpp:45:12: warning: comparison of integer expressions of different signedness: 'll' {aka 'long int'} and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |     if(c*2 > s.size())
      |        ~~~~^~~~~~~~~~

#include <bits/stdc++.h>

using namespace std;
using ll = int64_t;

int main() {
    string s;
    cin >> s;

    ll c = 0;
    stringstream ss;
    map<char, ll> mm;
    for(char c : s) { 
        if(mm.find(c) == mm.end())
            mm[c] = 0;
        mm[c]++;
    }


    priority_queue<pair<ll, char>> q;
    for(auto& e : mm) {
        q.emplace(e.second, e.first);
    }    

    while(!q.empty()) {
        auto chk = q.top();
        q.pop();

        if(!q.empty()) {
            auto chk2 = q.top();
            q.pop();
            if(chk.first == 0 || chk2.first == 0)
                throw runtime_error("NO");
            c++;
            chk2.first--;
            chk.first--;
            ss << chk.second << chk2.second << "\n";
            if(chk2.first != 0)
                q.emplace(chk2.first, chk2.second);
        }

        if(!q.empty() && chk.first != 0)
            q.emplace(chk.first, chk.second);
    }
    if(c*2 > s.size())
        throw runtime_error("NO");
    cout << c << "\n";
    cout << ss.str();
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 1, 2, 3

Verdict: ACCEPTED

Test 6

Group: 1, 2, 3

Verdict: ACCEPTED

Test 7

Group: 1, 2, 3

Verdict: ACCEPTED

Test 8

Group: 2, 3

Verdict: ACCEPTED

Test 9

Group: 2, 3

Verdict: ACCEPTED

Test 10

Group: 2, 3

Verdict: ACCEPTED

Test 11

Group: 2, 3

Verdict: ACCEPTED

Test 12

Group: 2, 3

Verdict: ACCEPTED

Test 13

Group: 2, 3

Verdict: ACCEPTED

Test 14

Group: 2, 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED

Test 16

Group: 3

Verdict: ACCEPTED

Test 17

Group: 3

Verdict: ACCEPTED

Test 18

Group: 3

Verdict: ACCEPTED

Test 19

Group: 3

Verdict: ACCEPTED

Test 20

Group: 3

Verdict: ACCEPTED

Test 21

Group: 3

Verdict: ACCEPTED