sliding window

Author: idf

340 Longest Substring with At Most K Distinct Characters.py

@@ -0,0 +1,47 @@
+"""
+Given a string, find the length of the longest substring T that contains at most k distinct characters.
+
+For example, Given s = "eceba" and k = 2,
+
+T is "ece" which its length is 3.
+
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+"""
+from collections import defaultdict
+
+__author__ = 'Daniel'
+
+
+class Solution(object):
+    def lengthOfLongestSubstringKDistinct(self, s, k):
+        """
+        Brute force: O(n^2 * n)
+
+        Sliding window O(n)
+        :type s: str
+        :type k: int
+        :rtype: int
+        """
+        st = 0  # start
+        counter = defaultdict(int)
+        maxa = 0
+        for idx, val in enumerate(s):
+            if counter[val] == 0:
+                k -= 1
+
+            counter[val] += 1
+            while k < 0:
+                counter[s[st]] -= 1
+                if counter[s[st]] == 0:
+                    k += 1
+                st += 1
+
+            maxa = max(maxa, idx - st + 1)
+
+        return maxa
+
+
+if __name__ == "__main__":
+    assert Solution().lengthOfLongestSubstringKDistinct("eceba", 2) == 3