AutoCorrect.cs

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

namespace Screen_N_Copy
{
    class AutoCorrect
    {
		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();
			}
		}
	}
}