Generate unique random numbers and sort them.

I'm trying to get 4 unique random numbers out of 1-50. For example, if I get (45,20,1,18), sort them to be (1,18,20,45).

However, my script generates 18 numbers and include the same numbers.

e.g. result{22.29.38.1.13.27.17.37.39.9.17.21.37.39.40.27.29.43} This time, double 17 and 37.

Could you help me to check my script? Why doesn't it work like I expect ?

I'd really appreciate your help!! Thank you.

  void Start(){

      List<int> fulNumList = new List<int>();
      List<int> pickedNumber = new List<int>();

 
      for (int i = 1; i < 50; i++) {
              fulNumList.Add(i);
      }
      //now all possible numbers are in fulNumList
 
      for (int i = 0; i < 3; i++) {
 
          int indexNum = Random.Range(0,fulNumList.Count);
          //get a random index number form 0-49
 
          int randomNum = fulNumList [indexNum];
 
          pickedNumber.Add(randomNum);
          //store randomNumber into pikedNumber list
              
          fulNumList.RemoveAt(indexNum);
          //remove the number that stored in pickedNumber from fulNumList for avoiding repeat numbers 
      }
 
      pickedNumber.Sort ();
 
      foreach (int result in pickedNumber){
          Debug.Log (result);
      }
 
  }