LC 0127 [H] Word Ladder

use a set so we can lookup and remove used words

shortest path BFS where the neighbors are swapping the char at the index and trying out every other letter in the alphabet

# ALPHABET = 'abcdefghijklmnopqrstuvwxyz'
ALPHABET = string.ascii_lowercase

class Solution:
    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
        wordList = set(wordList) # faster lookup and acts as visited set
        
        Q = deque([ [beginWord, 1] ])
        while Q:
            word, path_len = Q.popleft()
            
            if word == endWord:
                return path_len
            
            for i in range(len(word)):
                for c in ALPHABET:
                    neighbor_word = word[:i] + c + word[i+1:]
                    if neighbor_word in wordList:
                        wordList.remove(neighbor_word)
                        Q.append( [neighbor_word, path_len + 1] )
                        
        return 0