Problem Statement

A transformation sequence is a sequence that starts from the word beginWord, ends with endWord, and contains a word from the given dictionary wordList in the middle i.e. a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:

• Each adjacent pair of words differs by a single letter.
• Each si for 1 <= i <= k is in wordList. sk == endWord
• The beginWord does not need to be in wordList.

Given two strings, beginWord and endWord, and a wordList, return the number of words in the shortest transformation sequence from beginWord to endWord, or -1 if no such sequence exists.

Examples

• Example 1:

  • Input: startWord = "bit", endWord = "pog", wordList = ["but", "put", "pig", "pog", "big"]
  • Expected Output: 4
  • Justification: The shortest transformation sequenc is "bit" -> "big" -> "pig" -> "pog", which has 4 words.

• Example 2:

  • Input: startWord = "cat", endWord = "dog", wordList = ["cot", "dot", "dog"]
  • Expected Output: 4
  • Justification: The shortest transformation sequenc is "cat" -> "cot" -> "dot" -> "dog", which has 4 words.

• Example 3:

  • Input: startWord = "sing", endWord = "ring", wordList = ["ring"]
  • Expected Output: 2
  • Justification: The shortest transformation sequenc is "sing" -> "ring", which has 2 words.

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.

Try it yourself

Try solving this question here: