C# best way to check a list for duplicates code example

Example 1: c# find duplicates in list of strings

var list = new List<string>();
list.GroupBy(n => n).Any(c => c.Count() > 1);

Example 2: c# find duplicates in list

var query = lst.GroupBy(x => x)
              .Where(g => g.Count() > 1)
              .Select(y => y.Key)
              .ToList();