242. Word Ladder — BFS Shortest Transformation

Hard · Breadth-First Search

Given a `beginWord`, `endWord`, and a `wordList`, find the length of the shortest transformation sequence from `beginWord` to `endWord` where each step changes exactly one letter and every intermediate word must be in `wordList`. Return 0 if no path exists.

Examples

Example 1
Input: beginWord="hit", endWord="cog", wordList=["hot","dot","dog","lot","log","cog"]
Output: 5
Explanation: hit→hot→dot→dog→cog (length 5)

Constraints

• 1 ≤ words.length ≤ 5000, 1 ≤ word.length ≤ 10