Word Ladder

Given two words beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, such that:

• Only one letter can be changed at a time.
• Each transformed word must exist in the wordList.

Return 0 if no such sequence exists.

Note that beginWord does not need to be in wordList.

Examples

Example 1:

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

Output: 5

Explanation: One shortest transformation sequence is "hit" -> "hot" -> "dot" -> "dog" -> "cog", which has 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 no possible transformation.

Example 3:

Input: beginWord = "a", endWord = "c", wordList = ["a","b","c"]

Output: 2

Explanation: The shortest transformation is "a" -> "c", which has 2 words.

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 words in wordList are unique