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  1. using System;
  2. using System.Text.RegularExpressions;
  3.  
  4. public class Test
  5. {
  6.   public static void Main()
  7.   {
  8.     string s = "A B C C B C A D ABCD";
  9.  
  10.     foreach (Match m in Regex.Matches(s, @"\b(\w+)\b(?=.*\b\1\b)(?!.*\b\1\b.*\b\1\b)(?<!\b\1\b.+)", RegexOptions.IgnoreCase))
  11.       Console.WriteLine(m.Value);
  12.   }
  13. }
Success #stdin #stdout 0.06s 21364KB
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stdin
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Standard input is empty
stdout
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A
B
https://ideone.com/DnBUeA
language:
C# (gmcs 5.20.1)
created:
4 years ago
visibility:
public

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