mirror of
https://github.com/prdlk/leetcode.git
synced 2026-11-02 13:12:44 +00:00
68 lines
2.1 KiB
Plaintext
68 lines
2.1 KiB
Plaintext
---
|
|
title: '127. Word Ladder'
|
|
description: 'A transformation sequence from word beginWord to word endWord using a dictionary wordList is a sequence of words beginWord -> s1 -> s2 -> ... -> sk such that:'
|
|
sidebar:
|
|
label: 'Word Ladder'
|
|
badge: 'Hard'
|
|
---
|
|
|
|
<Badge variant="accent">Hash Table</Badge>
|
|
|
|
### Example 1:
|
|
- Input: `beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]`
|
|
- Output: `5`
|
|
- Explanation: One shortest transformation sequence is "hit" -> "hot" -> "dot" -> "dog" -> cog", which is `5` words long.
|
|
|
|
### Example 2:
|
|
- Input: `beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]`
|
|
- Output: `0`
|
|
- Explanation: The `endWord` "cog" is not in `wordList`, therefore there is no valid transformation sequence.
|
|
|
|
### 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.
|
|
|
|
## Solution
|
|
|
|
```py
|
|
import collections
|
|
|
|
|
|
class Solution:
|
|
def ladderLength(self, beginWord: str, endWord: str, wordList: list[str]) -> int:
|
|
if endWord not in wordList:
|
|
return 0
|
|
|
|
adj = collections.defaultdict(list)
|
|
wordList.append(beginWord)
|
|
|
|
for word in wordList:
|
|
for j in range(len(word)):
|
|
pattern = word[:j] + "*" + word[j + 1 :]
|
|
adj[pattern].append(word)
|
|
|
|
visit = set([beginWord])
|
|
q = collections.deque([beginWord])
|
|
res = 1
|
|
|
|
while q:
|
|
for i in range(len(q)):
|
|
word = q.popleft()
|
|
if word == endWord:
|
|
return res
|
|
for j in range(len(word)):
|
|
pattern = word[:j] + "*" + word[j + 1 :]
|
|
for adjWord in adj[pattern]:
|
|
if adjWord not in visit:
|
|
visit.add(adjWord)
|
|
q.append(adjWord)
|
|
res += 1
|
|
return 0
|
|
```
|