Word Ladder
Detailed guide and Python implementation for the 'Word Ladder' problem.
Problem Statement
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.
Write a function ladderLength(beginWord: str, endWord: str, wordList: List[str]) -> int.
- •1 <= len(beginWord) <= 10
- •endWord.length == beginWord.length
- •1 <= len(wordList) <= 5000
- •wordList[i].length == beginWord.length
- •beginWord, endWord, and wordList[i] consist of lowercase English letters
- •All the words in wordList are unique
Examples
beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
5
One shortest transformation sequence is "hit" -> "hot" -> "dot" -> "dog" -> "cog", which is 5 words long.
beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]
0
The endWord "cog" is not in wordList, so there is no valid transformation sequence.
Need a Hint?
Edge Cases to Watch
- Empty input structures
- Single element inputs
- Large numerical bounds
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