Word Ladder

class Solution:    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:        s = set(wordList)        l = list("abcdefghijklmnopqrstuvwxyz")        queue = deque([])        queue.append([beginWord,0])        while queue:            a, b = queue.popleft()            if a == endWord:                return b + 1            for j in range(len(a)):                for i in l:                    if (a[:j] + i + a[j+1:]) in s and (a[:j] + i +a[j+1:]) != beginWord:                        s.remove(a[:j]+i+a[j+1:])                        queue.append([a[:j]+i+a[j+1:],b+1])        return 0