添加 1002.查找常用字符.md Python3 使用collections.Counter实现

problems/1002.查找常用字符.md

@@ -193,6 +193,26 @@ class Solution:
                 hash[i] -= 1
         return result
 ```
+
+Python 3 使用collections.Counter
+```python
+class Solution:
+    def commonChars(self, words: List[str]) -> List[str]:
+        tmp = collections.Counter(words[0])
+        l = []
+        for i in range(1,len(words)):
+            # 使用 & 取交集
+            tmp = tmp & collections.Counter(words[i])
+
+        # 剩下的就是每个单词都出现的字符（键），个数（值）
+        for j in tmp:
+            v = tmp[j]
+            while(v):
+                l.append(j)
+                v -= 1
+        return l
+```
+
 javaScript
 ```js
 var commonChars = function (words) {