Merkkijono

input/code.cpp: In function 'int main(int, char**)':
input/code.cpp:15:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (auto ix = 0; ix < res.size(); ix += 2) {
                           ~~~^~~~~~~~~~~~

#include <iostream>

int main(int ac, char* av[]) {
    // syöte
    int n;
    std::cin >> n;

    // 1 <= n <= 16, eli tulos on
    // aina väh. "a"
    std::string res = "a";

    // iteroidaan syöte ja muodostetaan tulos
    for (auto i = 1; i < n; i++) {
        const auto c = static_cast<char>(97 + i);
        for (auto ix = 0; ix < res.size(); ix += 2) {
            res.insert(res.begin() + ix, c);
        }
        res += c;
    }

    std::cout << res << "\n";

    return 0;
}

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