# Leetcode 127 - Word ladder

`Note:`

- Looking for
`shortest`

path, use`BFS`

instead of`DFS`

. - Convert
`wordList`

into a`Set`

so we can quickly check if we’ve used a word before.

`Question:`

A `transformation sequence`

from word `beginWord`

to word `endWord`

using a dictionary `wordList`

is a sequence of words `beginWord -> s1 -> s2 -> ... -> sk`

such that:

- Every adjacent pair of words differs by a single letter.
- Every
`si`

for`1 <= i <= k`

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.

`Example:`

1 | Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"] |

`Code:`

1 | /** |