remove_dupes.cs

//
// Remove duplicate values from an array
//

Span<int> nums = new int[] { 0, 0, 6, 1, 2, 4, 6, 5, 2, 1, 0};

Span<T> remove_dupes<T>(Span<T> nums) where T : IEquatable<T>
{
    int unique_cursor = 0;
    for (int i = 0; i < nums.Length; i++)
    {
        for (int j = 0; j < nums.Length; j++)
        {
            if (i != j && nums[i].Equals(nums[j]))
            {
                // Was not unique
                goto NEXT_UP;
            }
        }

        T unique = nums[i];

        // Cursor will diverge from i if a dupe is found.
        if (unique_cursor != i)
        {   
            // Swap dupe with unique. Uniques left, dupes right.
            nums[i] = nums[unique_cursor];
        }

        nums[unique_cursor] = unique;
        unique_cursor++;

        NEXT_UP:
        continue;
    }

    return nums[..unique_cursor];
}

Console.WriteLine(string.Join(", ", nums.ToArray()));
Console.WriteLine(string.Join(", ", remove_dupes(nums).ToArray()));

// Output:
// 0, 0, 6, 1, 2, 4, 6, 5, 2, 1, 0
// 4, 5