Update 0242.有效的字母异位词.md

problems/0242.有效的字母异位词.md

@@ -138,7 +138,31 @@ class Solution:
                 return False
         return True
 ```
+Python写法二（没有使用数组作为哈希表，只是介绍defaultdict这样一种解题思路）：
 
+```python
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        from collections import defaultdict
+        
+        s_dict = defaultdict(int)
+        t_dict = defaultdict(int)
+        for x in s:
+            s_dict[x] += 1
+        
+        for x in t:
+            t_dict[x] += 1
+        return s_dict == t_dict
+```
+Python写法三(没有使用数组作为哈希表，只是介绍Counter这种更方便的解题思路)：
+
+```python
+class Solution(object):
+    def isAnagram(self, s: str, t: str) -> bool:
+        from collections import Counter
+        a_count = Counter(s)
+        b_count = Counter(t)
+        return a_count == b_count
 
 Go：