Merkkijono

#include <iostream>
#include <list>

using namespace std;

int main()
{
    int n;
    cin >> n;
    n--;

    list<char> tulos = {'a'};

    for (int i = 0; i < n; i++)
    {
        char lisattava = 98 + i;
        auto it = tulos.begin();
        int jatka = tulos.size() + 1;

        for (int k = 0; k < jatka; k++)
        {
            it--;
            tulos.insert(it, lisattava);
            it++;
            it++;
        }
    }

    for (char k : tulos)
        cout << k;
    cout << "\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

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED