Merkkijono

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

int main(){
    string alphabet = "abcdefghijklmnop";
    string tmp;
    int s;
    int n;
    string x = "a";
    cin >> n;

    for(int i=1; i<n;i++){
        s = x.length();
        for (int k = 0; k < 2*s; k++){
            tmp = alphabet[i];
            //cout << k;
            if(k>s){
                //x += tmp;
                //cout << "#";
                //x.insert((2*k)-1,tmp);
            }else{
                x.insert(2*k,tmp);
                //x.insert(0,"#");
            }
        }
        
    }
    //x.insert(0,"#");
    cout << x;
}

/*
a
bab
cbcacbc
dcdbdcdadcdbdcd
edecedebedecedeaedecedebedecede



*/

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