127. Word Ladder - LeetCode Solution

class Solution:
    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
        level = 1
        frontier = [beginWord]
        wle = set(wordList)
        al = "abcdefghijklmnopqrstuvwxyz"
        while frontier:
            next = []
            for cur in frontier:
                if cur==endWord:
                    return level
                for i in range(len(cur)):
                    for ch in al:
                        next_word = cur[:i]+ch+cur[i+1:]
                        if next_word in wle:
                            wle.remove(next_word)
                            next.append(next_word)
            frontier = next
            level+=1
        return 0