feat: word-ladder

Author: junbinding

bfs.word-ladder.py

@@ -0,0 +1,47 @@
+from typing import List
+from collections import deque
+
+class Solution:
+    """
+    127. 单词接龙
+    https://leetcode-cn.com/problems/word-ladder/description/
+    给定两个单词（beginWord 和 endWord）和一个字典，找到从 beginWord 到 endWord 的最短转换序列的长度。转换需遵循如下规则：
+    a - 每次转换只能改变一个字母。
+    b - 转换过程中的中间单词必须是字典中的单词。
+    https://leetcode-cn.com/problems/word-ladder/solution/python3-bfshe-shuang-xiang-bfsshi-xian-dan-ci-jie-/
+    """
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        st = set(wordList)
+        if endWord not in st:
+            return 0
+        m = len(beginWord)
+
+        queue = deque()
+        queue.append((beginWord, 1))
+
+        visited = set()
+        visited.add(beginWord)
+
+        while queue:
+            cur, step = queue.popleft()
+            if cur == endWord:
+                return step
+
+            for i in range(m):
+                for j in range(26):
+                    tmp = cur[:i] + chr(97 + j) + cur[i + 1:]
+                    if tmp not in visited and tmp in st:
+                        queue.append((tmp, step + 1))
+                        visited.add(tmp)
+
+        return 0
+
+
+so = Solution()
+# print(so.ladderLength('hit', 'cog', ["hot","dot","dog","lot","log","cog"]))
+# print(so.ladderLength('hot', 'dog', ["hot","dog"]))
+print(so.ladderLength('hot', 'dot', ["hot", "dot","dog"]))
+# print(so.ladderLength('a', 'c', ["a", "b","c"]))
+# print(so.ladderLength('hot', 'dog', ["hot", "dog","dot"]))
+
+