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82 lines
2.8 KiB
Plaintext
82 lines
2.8 KiB
Plaintext
---
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title: '127. Word Ladder'
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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:'
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icon: dot
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topics:
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- { name: "Hash Table", slug: "hash-table" }
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- { name: "String", slug: "string" }
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- { name: "Breadth-First Search", slug: "breadth-first-search" }
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- { name: "Bidirectional Search", slug: "bidirectional-search" }
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issue: "https://github.com/prdlk/leetcode/issues/138"
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companies:
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- { name: "Ola Cabs", period: "Thirty Days", frequency: 65.6 }
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- { name: "Amazon", period: "Thirty Days", frequency: 55.9 }
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- { name: "Google", period: "Thirty Days", frequency: 29 }
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- { name: "Apple", period: "Three Months", frequency: 69 }
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- { name: "Bloomberg", period: "Three Months", frequency: 46.8 }
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- { name: "Citadel", period: "Six Months", frequency: 88 }
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- { name: "LinkedIn", period: "Six Months", frequency: 69.8 }
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- { name: "Meta", period: "Six Months", frequency: 32.7 }
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sidebar:
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label: 'Word Ladder'
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badge: 'Hard'
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---
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### Example 1:
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- Input: `beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]`
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- Output: `5`
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- Explanation: One shortest transformation sequence is "hit" -> "hot" -> "dot" -> "dog" -> cog", which is `5` words long.
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### Example 2:
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- Input: `beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log"]`
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- Output: `0`
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- Explanation: The `endWord` "cog" is not in `wordList`, therefore there is no valid transformation sequence.
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### Constraints:
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- `1 <= beginWord.length <= 10`
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- `endWord.length == beginWord.length`
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- `1 <= wordList.length <= 5000`
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- `wordList[i].length == beginWord.length`
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- `beginWord`, `endWord`, and `wordList[i]` consist of lowercase English letters.
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- `beginWord != endWord`
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- All the words in `wordList` are unique.
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## Solution
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```py
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import collections
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class Solution:
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def ladderLength(self, beginWord: str, endWord: str, wordList: list[str]) -> int:
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if endWord not in wordList:
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return 0
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adj = collections.defaultdict(list)
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wordList.append(beginWord)
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for word in wordList:
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for j in range(len(word)):
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pattern = word[:j] + "*" + word[j + 1 :]
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adj[pattern].append(word)
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visit = set([beginWord])
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q = collections.deque([beginWord])
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res = 1
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while q:
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for i in range(len(q)):
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word = q.popleft()
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if word == endWord:
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return res
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for j in range(len(word)):
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pattern = word[:j] + "*" + word[j + 1 :]
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for adjWord in adj[pattern]:
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if adjWord not in visit:
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visit.add(adjWord)
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q.append(adjWord)
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res += 1
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return 0
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```
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