randomy.py

"""
Given two words (begin_word and end_word), and a dictionary's word list, return
the shortest transformation sequence from begin_word to end_word, such that:
Only one letter can be changed at a time.
Each transformed word must exist in the word list. Note that begin_word is not
a transformed word.
Note:
Return None if there is no such transformation sequence.
All words contain only lowercase alphabetic characters.
You may assume no duplicates in the word list.
You may assume begin_word and end_word are non-empty and are not the same.
"""
# Sample:
# begin_word = "hit"
# end_word = "cog"
# return: ['hit', 'hot', 'cot', 'cog']
# begin_word = "sail"
# end_word = "boat"
# ['sail', 'bail', 'boil', 'boll', 'bolt', 'boat']
# beginWord = "hungry"
# endWord = "happy"
# None