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  1. using System;
  2. using System.Collections.Generic;
  3.  
  4. public class Test
  5. {
  6. 	public static void Main()
  7. 	{
  8.         Console.WriteLine("Output {0}", returnSecondDuplicate(new[] { 'x', 'y', 'z', 'x', 'y' }));
  9.         Console.WriteLine("Output {0}",  returnSecondDuplicate(new[] { 'a', 'a', 'b', 'a', 'c', 'b', 'a', 'c', 'b' }));
  10.         Console.WriteLine("Output {0}", returnSecondDuplicate(new[] { 'a', 'a', 'a', 'b', 'a', 'c', 'b', 'a', 'c', 'b' }));
  11.         Console.ReadLine();
  12. 	}
  13.  
  14. 	public static char returnSecondDuplicate(char[] arr)
  15. 	{
  16. 		if (arr.Length == 0)
  17. 		    throw new ArgumentNullException("Empty Array passed");
  18. 		var dictionary = new Dictionary<char, int>();
  19. 		var duplicates = new List<char>();
  20. 		Char second = '\0';
  21. 		int i = 0;
  22.  
  23.         while (duplicates.Count != 2 && dictionary.Count != arr.Length)
  24.         {
  25.             if (!dictionary.ContainsKey(arr[i]))
  26.                 dictionary.Add(arr[i], 1);
  27.             else if (!duplicates.Contains(arr[i]))
  28.                 duplicates.Add(arr[i]); // only add duplicates once (ignoring any duplicate duplicates!)
  29.  
  30.             second = duplicates.Count == 2 ? arr[i] : second;
  31.             i++;
  32.         }
  33.  
  34.         return second;
  35. 	}
  36. }
Success #stdin #stdout 0.04s 34000KB
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https://ideone.com/PJ8tiL
language:
C# (gmcs 5.20.1)
created:
11 years ago
visibility:
public

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