add another solution

Author: sangheestyle

Python/longest-substring-with-at-most-k-distinct-characters.py

@@ -23,3 +23,27 @@ def lengthOfLongestSubstringKDistinct(self, s, k):
             longest = max(longest, i - start + 1)
         return longest
 
+
+# Time:  O(n)
+# Space: O(1)
+from collections import Counter
+
+
+class Solution2(object):
+    def lengthOfLongestSubstringKDistinct(self, s, k):
+        """
+        :type s: str
+        :type k: int
+        :rtype: int
+        """
+        counter = Counter()
+        left, max_length = 0, 0
+        for right, char in enumerate(s):
+            counter[char] += 1
+            while len(counter) > k:
+                counter[s[left]] -= 1
+                if counter[s[left]] == 0:
+                    del counter[s[left]]
+                left += 1
+            max_length = max(max_length, right-left+1)
+        return max_length