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127. Word Ladder

Description

A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words such that:

  • The first word in the sequence is beginWord.
  • The last word in the sequence is endWord.
  • Only one letter is different between each adjacent pair of words in the sequence.
  • Every word in the sequence is in wordList.

Given two words, beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.

 

Example 1:

Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
Output: 5
Explanation: One shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog" with 5 words.

Example 2:

Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]
Output: 0
Explanation: The endWord "cog" is not in wordList, therefore there is no possible transformation.

 

Constraints:

  • 1 <= beginWord.length <= 10
  • endWord.length == beginWord.length
  • 1 <= wordList.length <= 5000
  • wordList[i].length == beginWord.length
  • beginWord, endWord, and wordList[i] consist of lowercase English letters.
  • beginWord != endWord
  • All the strings in wordList are unique.

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