Pakkaus

#include <iostream>
#include <string>

int main() {
  std::string str;
  std::cin >> str;
  std::string res = "";
  std::string par;
  for (int i = 0; i < (int)str.size();) {
    // Get number of repetitions
    int k = i + 1;
    while((int)str[k] >= 48 && (int)str[k] <= 57) ++k;
    int v = 0;
    for (int d = i; d < k; ++d) {
      v *= 10;
      v += ((int)str[d]) - 48;
    }
    // Get string to repeat
    i = k;
    while(k < (int)str.size() && (int)str[k] > 57) ++k;
    par = str.substr(i, k - i);
    // Repeat to result
    for (int d = 0; d < v; ++d) {
      res.append(par);
    }
    i = k;
  }
  std::cout << res;
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED