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

namespace TextAnalysis
{
    static class SentencesParserTask
    {
        public static List<string> GetWords(string sentence)
        {
            var words = new List<string>();
            var word = new StringBuilder();
            foreach (var item in sentence)
            {
                if (item == '\''|| char.IsLetter(item))
                {
                    word.Append(char.ToLower(item));
                }
                else
                {
                    if (word.Length != 0)
                    {
                        words.Add(word.ToString());
                        word.Clear();
                    }
                }
            }
            if (word.Length != 0)
                words.Add(word.ToString());
            return words;
        }

        public static List<List<string>> ParseSentences(string text)
        {
            var sentencesArr = text.Split( '.', '!', '?', ';', ':', ')', '(' );
            var sentencesList = new List<List<string>>();
            foreach (var sentence in sentencesArr)
            {
                List<string> words = GetWords(sentence);
                if (words.Count != 0)
                {
                    sentencesList.Add(words);
                }
            }
            return sentencesList;
        }
    }
}