Given an array find the First duplicate element

string[] qwerty = { “Z”, “A”, “C”, “H”, “F”, “V”, “F”, “H”, “A” };

HashSet NoRepeat = new ();
string? first_repeat = null;
foreach (var item in qwerty)
{
if(!NoRepeat.Add(item))
{
first_repeat = item;
break;
}
}
Console.WriteLine(first_repeat);

var duplicates = arr.GroupBy(x => x).Select(x => x.Count() > 1);
return duplicates.First().key;

var duplicates = arr.GroupBy(x => x).Where(x => x.Count() });
return duplicates.First().key;

var duplicates = arr.GroupBy(x => x).Select(x => new { key = x.Key, val = x.Count() });
return duplicates.First().key;