Monistus

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

list<char> s;

int main(){
	cin.tie(0)->sync_with_stdio(0);
	string T;
	cin>>T;
	for(char u:T) s.push_back(u);
	for(auto it=s.begin();it!=s.end();){
		int c=*it;
		if('1'<=c&&c<='9'){
			c-='0';
			it=s.erase(it);
			auto a=it;
			auto e=it;
			for(int i=0;i<c;++i) ++e;
			for(int i=0;i<c;++i){
				s.emplace(e,*a);
				++a;
			}
		} else ++it;
	}
	for(char u:s) cout<<u;
	cout<<'\n';
}

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