Sukat

#include <iostream>
#include <string>
#include <vector>
#include <set>
#include <unordered_map>
using namespace std;

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

    unordered_map<char, int> amounts;
    for(auto c : s)
        amounts[c] += 1;

    set<pair<int, char>> pairs;
    for(auto p : amounts)
        pairs.insert({p.second, p.first});
              
    vector<string> ans;
    while(pairs.size() > 1){
        auto left = pairs.begin();
        auto right = pairs.end();
        right--;

        if(left == pairs.end() || right == pairs.end())
            break;

        string c;
        c += left -> second;
        c += right -> second;
        ans.push_back(c);

        pair<int, char> new_left = {left -> first - 1, left -> second};
        pair<int, char> new_right = {right -> first - 1, right -> second};
        
        pairs.erase(left);
        pairs.erase(right);
        if(new_left.first > 0)
            pairs.insert(new_left);
        if(new_right.first > 0)
            pairs.insert(new_right);
    }

    cout << ans.size() << "\n";
    for(auto s : ans){
        cout << s << "\n";
    }
}

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