Monistus

#include <iostream>
#include <string>
#include <stack>
using namespace std;

int main() {
    string w;
    cin >> w;
    string result = "";
    stack<char> s;
    for (int i = w.size() - 1; i >= 0; i--) s.push(w[i]);
    while (not s.empty()) {
        char c = s.top();
        s.pop();
        if (c >= '0' and c <= '9') {
            string k = "";
            int rep = c - '0';
            for (int i = 0; i < rep; i++) {
                k += s.top();
                s.pop();
            }
            for (int i = k.size() - 1; i >= 0; i--) s.push(k[i]);
            for (int i = k.size() - 1; i >= 0; i--) s.push(k[i]);
        }
        else result += c;
    }
    cout << result << endl;
}

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: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED