Update 159._Longest_Substring_with_At_Most_Two_Distinct_Characters.md

159._Longest_Substring_with_At_Most_Two_Distinct_Characters.md

@@ -9,5 +9,24 @@
 
 
 ```python
-
+class Solution(object):
+    def lengthOfLongestSubstringTwoDistinct(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        maps = {}
+        begin, end, counter, length = 0, 0, 0, 0
+        while end < len(s):
+            maps[s[end]] = maps.get(s[end], 0) + 1
+            if maps[s[end]] == 1:
+                counter += 1
+            end += 1
+            while counter > 2:
+                maps[s[begin]] -= 1
+                if maps[s[begin]] == 0:
+                    counter -= 1
+                begin += 1
+            length = max(length, end - begin)
+        return length
 ```