Merkkijono

#include <iostream>
#include <string>
using namespace std;

int main() {
    int i;
    cin >> i;
    string o1 = "a", o2;
    for (int a = 0; a < i - 1; a++)
    {
        o2 = o1;
        o1 = "";
        for (unsigned int b = 0; b < o2.size(); b++)
        {
            o1 += (char)(98 + a);
            o1 += o2[b];
        }
        o1 += (char)(98 + a);
    }
    cout << o1 << "\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