using System;
using System.Text;
using System.Collections.Generic;
public class Program
{
public static string removeNonDuplicate(string str) {
char[] arr = str.ToCharArray();
IList<char> duplicateList = new List<char>();
foreach (char ch in arr) {
if (str.IndexOf(ch) != str.LastIndexOf(ch)) {
duplicateList.Add(ch);
}
}
StringBuilder duplicateString = new StringBuilder();
foreach (char ch in duplicateList) {
duplicateString.Append(ch);
}
return duplicateString.ToString();
}
public static void Main(string[] args)
{
string str = "Bubble Occurrence Mammal c#";
Console.WriteLine(removeNonDuplicate(str));
}
}
/*
run:
ubble ccurrece ammal aa
*/
