Merkkijono

input/code.cpp: In function 'int main()':
input/code.cpp:22:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = 0; j < r.length(); j++) {
                   ~~^~~~~~~~~~~~

#include <bits/stdc++.h>

#define MIN(X, Y) (((X) <  (Y)) ? (X) : (Y))
#define MAX(X, Y) (((X) >= (Y)) ? (X) : (Y))

using namespace std;

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	int n;
	cin >> n;

	int i = 1;
	string r = "a";

	while (i < n) {
		char c = 97 + i;
		string s = "";
		s += c;
		for (int j = 0; j < r.length(); j++) {
			s += r[j];
			s += c;
		}
		r = s;
		i++;
	}

	cout << r;

	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