[Leetcode]127. Word Ladder@python

题目

Given two words (beginWord and endWord), and a dictionary’s word list, find the length of shortest transformation sequence from beginWord to endWord, such that:

Only one letter can be changed at a time
Each intermediate word must exist in the word list
For example,

Given:
beginWord = “hit”
endWord = “cog”
wordList = [“hot”,”dot”,”dog”,”lot”,”log”]
As one shortest transformation is “hit” -> “hot” -> “dot” -> “dog” -> “cog”,
return its length 5.

Note:
Return 0 if there is no such transformation sequence.
All words have the same length.
All words contain only lowercase alphabetic characters.

题目要求

给定两个单词，将单词1转变为单词2，每次转变只能改变一个字母，且改变后的单词要在单词表中出现。

解题思路

此题是参考了南郭子綦的思路。
采用了bfs的方式，每次改变单词中的一个字符，并判断生成的单词是否在wordlist中，直到生成目标单词，或者无法再继续下去。

代码

class Solution(object):
    def ladderLength(self, beginWord, endWord, wordList):
        """
        :type beginWord: str
        :type endWord: str
        :type wordList: Set[str]
        :rtype: int
        """
        q = [(beginWord,1)]
        while q:
            e,lens = q.pop(0)
            if e == endWord: return lens
            for i in range(len(e)):
                left = e[:i]
                right = e[i + 1:]
                for c in 'abcdefghigklmnopqrstuvwxyz':
                    if e[i] != c:
                        nextWord = left + c + right
                        if nextWord in wordList:
                            q.append((nextWord,lens + 1))
                            wordList.remove(nextWord)
        return 0