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;

string solve(string 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); 

//			cout << i << " " << digit << " " << before << " " << expanded << " " << after << endl;
//			cout << "key:" << digit << expanded <<endl;
			
			//store expanded + after in a hashmap
			s = solve(before + expanded + after); 
			//m[digit + expanded] =;
		}
	}

	return s;
}

int main() {
	string input; 
	cin >> input;
	string ans = solve(input);

	cout << ans << 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