Shortest Transformation Sequence

Given two words, start and end, and a dictionary containing an array of words, return the length of the shortest transformation sequence to transform start to end. A transformation sequence is a series of words in which:

• Each word differs from the preceding word by exactly one letter.
• Each word in the sequence exists in the dictionary.

If no such transformation sequence exists, return 0.

Example:

Input: start = 'red', end = 'hit',
       dictionary = [
            'red', 'bed', 'hat', 'rod', 'rad', 'rat', 'hit', 'bad', 'bat'
       ]
Output: 5

Constraints:

• All words are the same length.
• All words contain only lowercase English letters.
• The dictionary contains no duplicate words.