Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:
<li>Only one letter can be changed at a time.</li>
<li>Each transformed word must exist in the word list. Note that <em>beginWord</em> is <em>not</em> a transformed word.</li>
Note:
<li>Return 0 if there is no such transformation sequence.</li>
<li>All words have the same length.</li>
<li>All words contain only lowercase alphabetic characters.</li>
<li>You may assume no duplicates in the word list.</li>
<li>You may assume <em>beginWord</em> and <em>endWord</em> are non-empty and are not the same.</li>
Example 1:
Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"] Output: 5 Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog", return its length 5.
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.