leetcode-127-单词接龙

题目描述：

 

 官方题解：双向bfs O(mn) O(mn)

from collections import defaultdict
class Solution:
    def __init__(self):
        self.length = 0
        self.all_combo_dict = defaultdict(list)
    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
        if endWord not in wordList or not endWord or not beginWord or not wordList:
            return 0
        self.length = len(beginWord)
        for word in wordList:
            for i in range(self.length):
                self.all_combo_dict[word[:i] + '*' + word[i+1:]].append(word)
        queue_begin = [(beginWord,1)]
        queue_end = [(endWord,1)]
        visited_begin = {beginWord: 1}
        visited_end = {endWord: 1}
        ans = None
        while queue_begin and queue_end:
            ans = self.visitWordNode(queue_begin,visited_begin,visited_end)
            if ans:
                return ans
            ans =self.visitWordNode(queue_end,visited_end,visited_begin)
            if ans:
                return ans
        return 0
    def visitWordNode(self,queue,visited,others_visited):
        current_word,level = queue.pop(0)
        for i in range(self.length):
            intermediate_word = current_word[:i] + '*' +current_word[i+1:]
            for word in self.all_combo_dict[intermediate_word]:
                if word in others_visited:
                    return level+others_visited[word]
                if word not in visited:
                    visited[word] = level+1
                    queue.append((word,level +1))
        return 0