Word Ladder

hard

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 list wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or 0 if no such sequence exists.

Test Cases

Copy an input into the main harness and Run to verify

Input

beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]

Expected Output

5

Explanation: One shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog".

Input

beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]

Expected Output

0

Explanation: The endWord "cog" is not in wordList.

Constraints

1 <= beginWord.length <= 10
endWord.length == beginWord.length
1 <= wordList.length <= 5000
wordList[i].length == beginWord.length
beginWord, endWord, and wordList[i] consist of lowercase English letters.
beginWord != endWord
All the words in wordList are unique.

Hints

Hint 1 — click to reveal

Treat each word as a node; edges connect words that differ by one letter.

Hint 2 — click to reveal

BFS guarantees the shortest path — level by level.

Java Compiler