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64 lines
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Markdown
Executable File
64 lines
2.0 KiB
Markdown
Executable File
# [126. Word Ladder II](https://leetcode.com/problems/word-ladder-ii/)
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## 题目
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Given two words (*beginWord* and *endWord*), and a dictionary's word list, find all shortest transformation sequence(s) from *beginWord* to *endWord*, such that:
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1. Only one letter can be changed at a time
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2. Each transformed word must exist in the word list. Note that *beginWord* is *not* a transformed word.
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**Note:**
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- Return an empty list if there is no such transformation sequence.
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- All words have the same length.
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- All words contain only lowercase alphabetic characters.
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- You may assume no duplicates in the word list.
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- You may assume *beginWord* and *endWord* are non-empty and are not the same.
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**Example 1:**
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Input:
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beginWord = "hit",
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endWord = "cog",
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wordList = ["hot","dot","dog","lot","log","cog"]
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Output:
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[
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["hit","hot","dot","dog","cog"],
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["hit","hot","lot","log","cog"]
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]
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**Example 2:**
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Input:
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beginWord = "hit"
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endWord = "cog"
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wordList = ["hot","dot","dog","lot","log"]
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Output: []
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Explanation: The endWord "cog" is not in wordList, therefore no possible transformation.
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## 题目大意
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给定两个单词（beginWord 和 endWord）和一个字典 wordList，找出所有从 beginWord 到 endWord 的最短转换序列。转换需遵循如下规则：
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1. 每次转换只能改变一个字母。
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2. 转换过程中的中间单词必须是字典中的单词。
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说明:
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- 如果不存在这样的转换序列，返回一个空列表。
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- 所有单词具有相同的长度。
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- 所有单词只由小写字母组成。
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- 字典中不存在重复的单词。
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- 你可以假设 beginWord 和 endWord 是非空的，且二者不相同。
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## 解题思路
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- 这一题是第 127 题的加强版，除了找到路径的长度，还进一步要求输出所有路径。解题思路同第 127 题一样，也是用 BFS 遍历。
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- 当前做法不是最优解，是否可以考虑双端 BFS 优化，或者迪杰斯塔拉算法？
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