Monistus

#include<iostream>
#include<bits/stdc++.h>
#include<string> 
#include<map>
#include <unordered_map>
using namespace std;

typedef long long ll;
 
constexpr ll M = 1000000007;
constexpr ll P = (1 << 18);
constexpr int INF = 1e9;

//unordered_map<string, string> m;
//
vector<char> ans;

vector<char> solve(vector<char> s) {
	for (int i=0; i<(int)s.size(); i++) {
		char ch = s[i];
		int digit = ch - '0'; 

		if (digit > 0 && digit <= 9) {
			//string before = s.substr(0, i); 
			//string expanded = s.substr(i+1, digit); 
			//string after = s.substr(i+1); 
			vector<char> before(s.begin(), s.begin()+i);
			ans.insert(ans.end(), before.begin(), before.end());

			vector<char> expanded(&s[i+1], &s[i+1]+digit);
			vector<char> after(&s[i+1], &s.back()+1); 
//			cout << i << " " << digit << " " << before << " " << expanded << " " << after << endl;
//			cout << "key:" << digit << expanded <<endl;
//
			//store expanded + after in a hashmap
			expanded.insert(expanded.end(), after.begin(), after.end());

			return solve(expanded);
		}
	}

	return s;
}

int main() {
	string input; 
	cin >> input;

	vector<char> arr(input.begin(), input.end());

	vector<char> res = solve(arr);

	ans.insert(ans.end(), res.begin(), res.end());

	for (auto ch : ans) cout << ch;
	cout << 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: 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