Monistus

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

string random_string(size_t length) {
    const string CHARACTERS = "12abcdefghijklmnopqrstuvwxyz";

    random_device random_device;
    mt19937 generator(random_device());
    uniform_int_distribution<> distribution(0, CHARACTERS.size() - 1);

    string random_string;

    for (size_t i = 0; i < length; ++i)
    {
        random_string += CHARACTERS[distribution(generator)];
    }

    return random_string;
}

string fast(string s) {
    string new_s = "";
    for (int k = 0; k < 2; ++k) {
        for (int i = 0; i < (int)s.size(); ++i) {
            if (isdigit(s[i])) {
                int d = (s[i]-'0');
                string dup = "";
                for (int j = i+1; j <= d+i; ++j) {
                    dup += s[j];
                }
                new_s += dup;
            }
            else 
                new_s += s[i];
        }
        s = new_s;
        new_s = ""; 
    }
    return s;
}

string brute(string s) {
    for (int i = 0; i < (int) s.size(); ++i) {
        if (isdigit(s[i])) {
            string temp = "";
            for (int j = 0; j < i; ++j) temp += s[j];
            for (int j = i+1; j <= i+(s[i]-'0'); ++j) temp += s[j];
            for (int j = i+1; j < (int) s.size(); ++j) temp += s[j];
            s = temp;
            i = -1;
        }
    }
    return s;
}

int main() {
    string s1 = "", s2 = "", s3;
    cin >> s3;
    if (s3.size() <= 20) {
        cout << brute(s3);
        return 0;
    }
    else {
        cout << fast(s3);
        return 0;
    }
    while (s1 == s2) {
        s3 = random_string(4);
        s1 = fast(s3);
        s2 = brute(s3);
    }
    cout << s1 << '\n' << s2 << '\n' << s3;
}

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: WRONG ANSWER

Test 9

Group: 2

Verdict: WRONG ANSWER

Test 10

Group: 2

Verdict: WRONG ANSWER

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: WRONG ANSWER

Test 13

Group: 2

Verdict: WRONG ANSWER

Test 14

Group: 2

Verdict: WRONG ANSWER