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花花酱 LeetCode 127. Word Ladder

https://leetcode.com/problems/word-ladder/description/

Problem:

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:

  1. Only one letter can be changed at a time.
  2. Each transformed word must exist in the word list. Note that beginWord is not a transformed word.

For example,

Given:
beginWord = "hit"
endWord = "cog"
wordList = ["hot","dot","dog","lot","log","cog"]

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.
  • You may assume no duplicates in the word list.
  • You may assume beginWord and endWord are non-empty and are not the same.

 

Idea:



BFS

Time Complexity: O(n*26^l) -> O(n*26^l/2), l = len(word), n=|wordList|

Space Complexity: O(n)



Solution 1: BFS

C++

Java

Solution 2: Bidirectional BFS

C++

Java

Python

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