Merge pull request #1178 from ericL1u/master

127题 增加python解法

problems/0127.单词接龙.md

@@ -134,7 +134,29 @@ public int ladderLength(String beginWord, String endWord, List<String> wordList)
 ```
 
 ## Python 
-
+```
+class Solution:
+    def ladderLength(self, beginWord: str, endWord: str, wordList: List[str]) -> int:
+        wordSet = set(wordList)
+        if len(wordSet)== 0 or endWord not in wordSet:
+            return 0
+        mapping = {beginWord:1}
+        queue = deque([beginWord]) 
+        while queue:
+            word = queue.popleft()
+            path = mapping[word]
+            for i in range(len(word)):
+                word_list = list(word)
+                for j in range(26):
+                    word_list[i] = chr(ord('a')+j)
+                    newWord = "".join(word_list)
+                    if newWord == endWord:
+                        return path+1
+                    if newWord in wordSet and newWord not in mapping:
+                        mapping[newWord] = path+1
+                        queue.append(newWord)                      
+        return 0
+```
 ## Go 
 
 ## JavaScript