Monistus

#include<bits/stdc++.h>
using namespace std;
using ll = long long;

bool k = false;
int q = 0;

string haku(string s){

    if(k) return s;

    string m = "";

    int n = s.size();
    for(int i = 0; i < n; i++){

        char c = s[i];
        
        if(isdigit(c) && !k){

            int x = c - '0';

            if(i < n-x){

                string u = s.substr(i + 1, x);
                u = haku(u);
                m += u;

            }
            else{

                k = true;
                q = i;
                m += c;

            }

        }
        else{
            if(k){
                m += s.substr(i, n);
                return m;
            }
            else m += c;
        }

    }

    return m;

}


int main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    
    
    string s;
    cin >> s;

    do{
        k = false;
        s = haku(s);
    } while(k);

    cout << s;

    
}

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: TIME LIMIT EXCEEDED

Test 10

Group: 2

Verdict: TIME LIMIT EXCEEDED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED