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/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class Program
{
	public static void Main()
	{
		var last = "CamelCase".SplitBy(char.IsUpper).Last();
		Console.WriteLine(last);
	}
}

public static class StringHelper
{
	public static IEnumerable<string> SplitBy(this string source, Func<Char, bool> predicate)
	{
		if (source == null)
			throw new ArgumentNullException("source");
		
		if (predicate == null)
			throw new ArgumentNullException("predicate");
		
		var sb = new StringBuilder();
		
		foreach (var ch in source)
		{
			if (predicate(ch))
			{
				if (sb.Length != 0)
					yield return sb.ToString();
				sb.Clear();
				sb.Append(ch);
			}
			else
			{
				sb.Append(ch);
			}
		}

		yield return sb.ToString();
	}
}