Word Ladder

Given two words (beginWord and endWord), and a dictionary's word list, find the length of 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 word list. Note: Return 0 if there is no such transformation sequence. All words have the same length. All words contain only lowercase alphabetic characters. You may assume beginWord and endWord are non-empty and are not the same. Example: Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"] Output: 5 Explanation: One shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog", which is 5 words long. Example Input hit cog hot cog dot dog lot log