unity random range not repeat code example

Example 1: random.range unity not working

//Do u have using System too? If so u have to specify w
UnityEngine.Random.Range(1, 10);

Example 2: how to never have 2 same values from random function in unity

List<int> usedValues = new List<int>();
 public int UniqueRandomInt(int min, int max)
 {
     int val = Random.Range(min, max);
     while(usedValues.Contains(val))
     {
         val = Random.Range(min, max);
     }
     return val;
 }

Example 3: unity random range int not working

float rand = UnityEngine.Random.Range(0, 4);              Debug.Log(rand);