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 before; 
int seenCount;
 
string solve(string s) {
	if (m.count(s)) {
		seenCount++;
		return m[s];	
	}

	for (int i=0; i<(int)s.size(); i++) {
		char ch = s[i];
		int digit = ch - '0'; 
 
		if (digit > 0 && digit <= 9) {
			string b4 = s.substr(0, i); 
			string expanded = s.substr(i+1, digit); 
			string after = s.substr(i+1); 
 
			//if (m.count(expanded)) {
			//	seenCount++;
			//	return m[expanded] + solve(after);
			//}

			//string s1 = solve(expanded + );
			//string s2 = solve(after);
			//m[expanded] = s1;

			string ans = solve(expanded + after);
			m[s] = b4 + ans;

			return m[s];
		}
	}
 
	return s;
}
 
int main() {
	string input; 
	cin >> input;
	string ans = solve(input);

	//for (auto x : m) {
	//	cout << x.first << " " << x.second << endl;
	//}
	//cout << seenCount << endl;
 
	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