code: def bfs(self, forward, backward, wordlist, level):
      if len(forward) == 0 or len(backward) == 0:
          return 0
      if len(forward) > len(backward):
          return self.bfs(backward, forward, wordlist, level)
      is_connected = False
      next_level = set()
      for word in forward:
          for c in string.ascii_lowercase:
              for index in range(len(word)):
                  neigh = word[:index] + c + word[index + 1 :]
                  if neigh in backward:
                      is_connected = True
                      return level
                  if not is_connected and neigh in wordlist:
                      next_level.add(neigh)
                      wordlist.discard(neigh)
      if not is_connected:
          return self.bfs(next_level, backward, wordlist, level + 1)
  
imports: import string
label_desc: Use image node_id 2 for calling the Solution obj's underlying member method code with example usage: obj.bfs(forward, backward, wordlist, level) and returns: int, self, self, level