CODE

public class Solution {
  List<string> foundWords = new List<string>();
  List<List<int>> processed = new List<List<int>>();   
  bool wordFound = false;
  public List<string> FindWords(char[][] board, string[] words) {
    foreach (var w in words)
    {
      wordFound = false;
      for (int i = 0; i < board.Length; i++)
      {
        for (int j = 0; j < board[0].Length; j++)
        {
          if (board[i][j] == w[0])
          {
            processed.Clear();
            bool found = search(board, i, j, w, 0);
            if (found)
            {
              foundWords.Add(w);
              break;
            }
          }
        }
        if (wordFound)
          break;
      }
    }
    return foundWords;        
  }


  bool search(char[][] board, int row, int col, string word, int ind)
  {
    if (ind < word.Length)
      Console.WriteLine(word + ": " + word[ind]);
    if (ind == word.Length)
    {
      wordFound = true;
      return wordFound;
    }
    List<int> c = new List<int>();
    c.Add(row); c.Add(col);
    processed.Add(c);

    if (board[row][col] == word[ind++])
    {
      if (row < board.Length-1 && !alreadyChecked(row+1, col) && !wordFound)
        search(board, row+1, col, word, ind);
      if (col > 0 && !alreadyChecked(row, col-1) && !wordFound)
        search(board, row, col-1, word, ind);
      if (col < board[0].Length-1 && !alreadyChecked(row, col+1) && !wordFound)
        search(board, row, col+1, word, ind);
      if (row > 0 && !alreadyChecked(row-1, col) && !wordFound)
        search(board, row-1, col, word, ind);
      
      if (ind == word.Length)
        wordFound = true;
    }
    processed.Remove(c);
    return wordFound;
  }

  bool alreadyChecked(int row, int col)
  {
    foreach (var l in processed)
      if (l[0] == row && l[1] == col)
        return true;
    return false;
  }
}