def ladderLength(self, beginWord, endWord, wordList):

"""

if endWord not in wordList or not endWord or not beginWord or not wordList:

return 0

wordLen = len(beginWord)

allComboDict = defaultdict(list)

for word in wordList:

for i in range(wordLen):

allComboDict[word[:i] + "*" + word[i + 1:]].append(

word) # Creating the adjacency list of . the intermediate nodes/words. Every Node has 3 intermediate nodes

queue = deque([(beginWord, 1)])

visited = {beginWord: True}

while queue:

currentWord, level = queue.popleft() # Here the words are the nodes

for i in range(wordLen):

intermediateWord = currentWord[:i] + "*" + currentWord[

i + 1:] # here the words are the . intermediate nodes. Every Node has 3 intermediate nodes. And here, the nodes doesn't have the adjacency list. The intermediate node has it.

for word in allComboDict[intermediateWord]:

if word == endWord:

return level + 1

if word not in visited:

visited[word] = True

queue.append((word, level + 1))

allComboDict[intermediateWord] = []

def ladderLength(self, beginWord, endWord, wordList):

"""

if endWord not in wordList or not endWord or not beginWord or not wordList:

return 0

wordLen = len(beginWord)

letterToWordMap = defaultdict(list)

wordList.append(beginWord)

for word in wordList:

for i in range(wordLen):

pattern = word[:i] + "*" + word[i + 1:]

letterToWordMap[pattern].append(word)

graph = defaultdict(list)

for word in wordList:

for i in range(wordLen):

pattern = word[:i] + "*" + word[i + 1:]

nodeList = letterToWordMap[pattern]

graph[word].extend(nodeList)

queue = deque([(beginWord, 1)])

visited = set()

visited.add(beginWord)

while queue:

currentLevelSize = len(queue)

while currentLevelSize > 0:

currentWord, level = queue.popleft()

currentLevelSize -= 1

for neighbours in graph[currentWord]:

if neighbours == endWord:

return level + 1

else:

if neighbours not in visited:

visited.add(neighbours)

queue.append((neighbours, level + 1))