Monistus

#include <iostream>
#include <vector>

using namespace std;

string duplicate(string &str)
{
    bool finalWord = true;
    int index = 0;
    string newWord = "";
    for (char ch : str)
    {
        if (isdigit(ch))
        {
            finalWord = false;
            string first_part = "";
            if (index > 0)
            {
                first_part = str.substr(0, index);
            }
            string second_part = str.substr(index + 1, str.length() - 1 - index);
            string dup_part = str.substr(index + 1, int(ch) - 48);
            newWord = first_part + dup_part + second_part;
            break;
        }
        index++;
    }
    if (finalWord)
    {
        return str;
    }
    else
    {
        return duplicate(newWord);
    }
}

int main()
{
    string word;
    cin >> word;
    cout << duplicate(word);
    return 0;
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 1, 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED

Test 5

Group: 1, 2

Verdict: ACCEPTED

Test 6

Group: 1, 2

Verdict: ACCEPTED

Test 7

Group: 1, 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: RUNTIME ERROR

Test 9

Group: 2

Verdict: RUNTIME ERROR

Test 10

Group: 2

Verdict: RUNTIME ERROR

Test 11

Group: 2

Verdict: RUNTIME ERROR

Test 12

Group: 2

Verdict: RUNTIME ERROR

Test 13

Group: 2

Verdict: RUNTIME ERROR

Test 14

Group: 2

Verdict: RUNTIME ERROR