How do I check if my array has repeated values inside it?

Question

So here is my array.

double[] testArray = new double[10];
// will generate a random numbers from 1-20, too lazy to write the code

I want to

Answer 1

use a hashset to add members to, then check if there a previous occurrence of current member

public bool ContainsDuplicate(double[] nums) 
{
            int size = nums.Length;
            HashSet set1 = new HashSet();

            for (int i = 0; i < size; i++)
            {
                if (set1.Contains(nums[i]))
                {
                    return true;
                }
                else
                {
                    set1.Add(nums[i]);
                }
            }
            return false;
}