How to Write a Spelling Corrector in C# (from Peter Norvig's Python example)

NorvigSpellChecker.cs

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

namespace SpellingCorrector
{
  	/// <summary>
	/// Conversion from http://norvig.com/spell-correct.html by C.Small
	/// </summary>
	public class Spelling
	{
		private Dictionary<String, int> _dictionary = new Dictionary<String, int>();
		private static Regex _wordRegex = new Regex("[a-z]+", RegexOptions.Compiled);

		public Spelling()
		{
			string fileContent = File.ReadAllText("big.txt");
			List<string> wordList = fileContent.Split(new string[] {"\n"} , StringSplitOptions.RemoveEmptyEntries).ToList();

			foreach (var word in wordList)
			{
				string trimmedWord = word.Trim().ToLower();
				if (_wordRegex.IsMatch(trimmedWord))
				{
					if (_dictionary.ContainsKey(trimmedWord))
						_dictionary[trimmedWord]++;
					else
						_dictionary.Add(trimmedWord, 1);
				}
			}
		}

		public string Correct(string word)
		{
			if (string.IsNullOrEmpty(word))
				return word;
			
			word = word.ToLower();

			// known()
			if (_dictionary.ContainsKey(word))
				return word;

			List<String> list = Edits(word);
			Dictionary<string, int> candidates = new Dictionary<string, int>();

			foreach (string wordVariation in list)
			{
				if (_dictionary.ContainsKey(wordVariation) && !candidates.ContainsKey(wordVariation))
					candidates.Add(wordVariation, _dictionary[wordVariation]);
			}

			if (candidates.Count > 0)
				return candidates.OrderByDescending(x => x.Value).First().Key;

			// known_edits2()
			foreach (string item in list)
			{
				foreach (string wordVariation in Edits(item))
				{
					if (_dictionary.ContainsKey(wordVariation) && !candidates.ContainsKey(wordVariation))
						candidates.Add(wordVariation, _dictionary[wordVariation]);
				}
			}

			return (candidates.Count > 0) ? candidates.OrderByDescending(x => x.Value).First().Key : word;
		}

		private List<string> Edits(string word)
		{
			var splits = new List<Tuple<string, string>>();
			var transposes = new List<string>();
			var deletes = new List<string>();
			var replaces = new List<string>();
			var inserts = new List<string>();

			// Splits
			for (int i = 0; i < word.Length; i++)
			{
				var tuple = new Tuple<string, string>(word.Substring(0, i), word.Substring(i));
				splits.Add(tuple);
			}

			// Deletes
			for (int i = 0; i < splits.Count; i++)
			{
				string a = splits[i].Item1;
				string b = splits[i].Item2;
				if (!string.IsNullOrEmpty(b))
				{
					deletes.Add(a + b.Substring(1));
				}
			}

			// Transposes
			for (int i = 0; i < splits.Count; i++)
			{
				string a = splits[i].Item1;
				string b = splits[i].Item2;
				if (b.Length > 1)
				{
					transposes.Add(a + b[1] + b[0] + b.Substring(2));
				}
			}

			// Replaces
			for (int i = 0; i < splits.Count; i++)
			{
				string a = splits[i].Item1;
				string b = splits[i].Item2;
				if (!string.IsNullOrEmpty(b))
				{
					for (char c = 'a'; c <= 'z'; c++)
					{
						replaces.Add(a + c + b.Substring(1));
					}
				}
			}

			// Inserts
			for (int i = 0; i < splits.Count; i++)
			{
				string a = splits[i].Item1;
				string b = splits[i].Item2;
				for (char c = 'a'; c <= 'z'; c++)
				{
					inserts.Add(a + c + b);
				}
			}

			return deletes.Union(transposes).Union(replaces).Union(inserts).ToList();
		}
	}
}

Why u use so many cycles? And what the reason to use Dictionary<string, int> if u can just use HashSet?

I optimized your programm, come here to see it: https://gist.github.com/nestquik/6c5146c75631a8ff3084