Merkkijono

#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n;
    cin >> n;
    string s = "abcdefghijklmnopqrstuvwxyz";
    vector<char> aakkoset(s.begin(), s.end());

    vector<char> output;

    for (int i = 0; i < n; i++)
    {
        char kirjain = aakkoset[i];
        int koko = output.size();
        for (int j = 0; j < koko + 1; j++)
        {
            output.insert(output.begin() + 2 * j, kirjain);
        }
    }
    for (auto x : output)
    {
        cout << x;
    }
    cout << endl;
}

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