Monistus

#include<bits/stdc++.h>
using namespace std;
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
using ll = long long;
 
 
int main() {
 
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    string s;
    cin >> s;
 
    stack<char> st;
    reverse(all(s));
    for (char c : s) st.push(c);
 
    while (!st.empty()) {
        char c = st.top();
        st.pop();
        if (c >= '1' && c <= '9') {
            int d = c - '1' + 1;
            vector<char> v;
            while (d--) {
                v.push_back(st.top());
                st.pop();
            }
            reverse(all(v));
            for (char u : v) st.push(u);
            for (char u : v) st.push(u);
        }
        else cout << c;
    }
 
    cout << "\n";
 
    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: 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