Word Ladder Leetcode optimised 2 solutions c++ code and explanation

A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord Every adjacent pair of words differs by a single letter. Every si is in wordList. Note that beginWord does not need to be in wordList. sk == endWord Given two words, beginWord and endWord, and a dictionary wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.