Word Ladder (Shortest Transformation)

Problem Given beginWord, endWord, and a word list, find the length of the shortest transformation sequence from beginWord to endWord, changing exactly one letter at a time, where every intermediate word must be in the list. Return 0 if no such sequence exists.

Input / Output

• Input: beginWord, endWord, and wordList (all the same length).
• Output: the number of words in the shortest transformation sequence (including both ends), or 0.

Constraints

• 1 ≤ wordList ≤ 5000; all words are the same length.
• Only words present in the list count as valid intermediate steps.

Example

• hit → cog via [hot,dot,dog,lot,log,cog] → 5 (hit → hot → dot → dog → cog).