CODE

public class Solution {
  public List<List<string>> GroupAnagrams(string[] strs) {
    List<List<string>> anagramGroups = new List<List<string>>();
    for (int i = 0; i < strs.Length; i++) {
      List<string> otherWords = new List<string>();
      otherWords.AddRange(strs);
      otherWords.RemoveRange(0, i + 1);

      List<string> anagrams = new List<string>();

      /* if word not already in anagram groups, get its anagrams */
      if (!checkGroupsForExisting(strs[i], anagramGroups)) {
        anagrams = GetAnagrams(strs[i], otherWords);
        anagramGroups.Add(anagrams);
      }
    }
    return anagramGroups;
  }

  /* get all anagrams in list for given word */
  private List<string> GetAnagrams(string word, List<string> otherWords) {
    List<string> anagrams = new List<string>();

    /* last word in list - single: add to anagrams and return */
    if (otherWords.Count == 0) {
      anagrams.Add(word);
      return anagrams;
    }

    /* check if original word has already been added to anagrams */
    bool dupAlreadyAdded = false;

    for (int i = 0; i < otherWords.Count; i++) {
      /* skip if not same length */
      if (word.Length != otherWords[i].Length)
        continue;

      /* if same word encountered, add both to anagrams list */
      if (word.Equals(otherWords[i])) {
        /* only add orig word if it hasn't been added yet */
        if (!dupAlreadyAdded) {
          anagrams.Add(word);
          dupAlreadyAdded = true;
        }
        anagrams.Add(word);
        continue;
      }

      char[] word_letters = new char[word.Length];
      char[] othWord_letters = new char[otherWords[i].Length];

      for (int j = 0; j < word.Length; j++) {
        word_letters[j] = word[j];
        othWord_letters[j] = otherWords[i][j];
      }

      /* sort and compare the letters of both words */
      Array.Sort(word_letters);
      Array.Sort(othWord_letters);

      bool wordsMatch = true;

      for (int j = 0; j < word.Length; j++) {
        if (word_letters[j] != othWord_letters[j]) {
          wordsMatch = false;
          break;
        }
      }

      /* not an anagram, continue to next word in list */
      if (!wordsMatch)
        continue;

      /* otherwise, an anagram - add both if not already in the list */
      if (!anagrams.Contains(word))
        anagrams.Add(word);
      if (!anagrams.Contains(otherWords[i]))
        anagrams.Add(otherWords[i]);
    }

    /* if no anagrams found, just add the word as its own anagram */
    if (anagrams.Count == 0)
      anagrams.Add(word);

    return anagrams;
  }

  /* check if a word is already in anagram groups to exclude it */
  bool checkGroupsForExisting(string word, List<List<string>> groups) {
    for (int i = 0; i < groups.Count; i++) {
      for (int j = 0; j < groups[i].Count; j++) {
        if (groups[i][j].Equals(word))
          return true;
      }
    }
    return false;
  }
}