Merkkijono

var readline = require('readline');
var r = readline.createInterface({
    input: process.stdin,
    output: process.stdout,
    terminal: false
});

function merkkijono(n) {
    const abc = 'abcdefghijklmnopqrstuvwxyz';
    let result = [];
    for (let i = 0; i < n; i++) {
        const c = abc[i];
        let newResult = []
        for (let v of result) {
            newResult.push(c);
            newResult.push(v);
        }
        result = [...newResult, c];
    }
    console.log(result.join(''));
}

r.on('line', function (line) {
    merkkijono(parseInt(line));
});

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