Hard
Quiz
#126 Word Ladder II
APPROACH
A transformation sequence from beginWord to endWord using dictionary wordList is a chain beginWord -> s1 -> s2 -> ... -> sk where:
- Each consecutive pair of words differs by exactly one letter.
- Every intermediate word si (for 1 <= i <= k) must appear in wordList. The beginWord does not need to be in wordList.
- sk == endWord
Return all shortest transformation sequences from beginWord to endWord, or an empty list if none exist. Each sequence should be given as [beginWord, s1, s2, ..., sk].
Example 1:
Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
Output: [["hit","hot","dot","dog","cog"],["hit","hot","lot","log","cog"]]
Explanation: There are 2 shortest transformation sequences:
"hit" -> "hot" -> "dot" -> "dog" -> "cog"
"hit" -> "hot" -> "lot" -> "log" -> "cog"
Example 2:
Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]
Output: []
Explanation: The endWord "cog" is not in wordList, therefore there is no valid transformation sequence.
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What is the optimal approach for this problem?