How to check repeated letters in a string c#

Question

I am creating a program that checks repeated letters in a string.

For Example:

wooooooooooow
happpppppppy

This is my

Answer 1

To find duplicate or repeated letters in given string using C#

string str = "Welcome Programming";
char[] Array = str.ToCharArray();
var duplicates = Array.GroupBy(p => p).Where(g => g.Count() > 1).Select(g => g.Key).ToList();
string duplicateval= string.Join(",", duplicates.ToArray());

Output:

e,o,m,r,g