Merkkijono

input/code.cpp: In function 'std::__cxx11::string operate(std::__cxx11::string, int)':
input/code.cpp:18:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < in.length(); i++){
                    ~~^~~~~~~~~~~~~

#include <iostream>
#include <string>

using namespace std;

int pow(int b, int e) {
    int r = 1;
    for (int i = 0; i < e; i++){
        r = r * b;
    }
    return r;
}

string operate(string in, int rn){
    //cout << "round number " << rn << "\n";
    string ne (pow(2,rn)-1, 'a'+rn-1);
    //cout << "base string: " << ne << "\n";
    for(int i = 0; i < in.length(); i++){
        //cout << "moving " << i << ": " << in[i] << " to " << 2*i+1 << "\n";
        ne[2*i+1] = in[i];
    }

    return ne;
}

int main() {
    int n;
    cin >> n;

    string str = "a";

    for (int i = 0; i < n; i++) {
        str = operate(str, i+1);
        //cout << str << "\n";
    }

    cout << str;

    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