Flutter dart generates a list of random numbers that are not repeated in n intervals

    List<int> resultList = [];
    var rng = new Random();
    int count = 0;
    while (count < 6) {
                    // Generate 6 individual 
      int index = rng.nextInt(12) + 1; // 1-12 Between 
      if (!resultList.contains(index)) {
    
        resultList.add(index);
        count++;
      }
    }
    resultList.sort();
    print(resultList);