text: # Design a data structure that supports the following two operations:
  #
  # void addWord(word)
  # bool search(word)
  # search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.
  #
  # Example:
  #
  # addWord("bad")
  # addWord("dad")
  # addWord("mad")
  # search("pad") -> false
  # search("bad") -> true
  # search(".ad") -> true
  # search("b..") -> true
  # Note:
  # You may assume that all words are consist of lowercase letters a-z.
  
  class TrieNode:
      def __init__(self):
          self.is_word = False
          self.children = dict()
  
  
  class WordDictionary:
      def __init__(self):
          """
          Initialize your data structure here.
          """
          self.root = TrieNode()
  
      def addWord(self, word):
          """
          Adds a word into the data structure.
          :type word: str
          :rtype: void
          """
          root = self.root
          for ch in word:
              if ch not in root.children:
                  root.children[ch] = TrieNode()
              root = root.children[ch]
          root.is_word = True
  
      def search(self, word):
          """
          Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
          :type word: str
          :rtype: bool
          """
          root = self.root
          return self.dfs(root, word, 0)
  
      def dfs(self, node, word, index):
          if index == len(word) - 1:
              if word[index] != '.' and word[index] in node.children and node.children[word[index]].is_word:
                  return True
              elif word[index] == '.' and any(node.children[child].is_word for child in node.children):
                  return True
              else:
                  return False
          else:
              if word[index] == '.':
                  return any(self.dfs(node.children[child], word, index + 1) for child in node.children)
              elif word[index] in node.children:
                  return self.dfs(node.children[word[index]], word, index + 1)
              else:
                  return False
  
  
                  # Your WordDictionary object will be instantiated and called as such:
                  # obj = WordDictionary()
                  # obj.addWord(word)
                  # param_2 = obj.search(word)
  
  
  s = WordDictionary()
  s.addWord('bad')
  s.addWord('dad')
  s.addWord('mad')
  print(s.search('pad'))
  print(s.search('bad'))
  print(s.search('.ad'))
  print(s.search('b..'))
  print(s.search('c..'))
  print(s.search('...'))