solve: longestRepeatingCharacterReplacement

Author: GaggleHelena

longest-repeating-character-replacement/yolophg.py

@@ -0,0 +1,27 @@
+# Time Complexity: O(n) - loop through the string once, and operations like `max(count.values())` are constant time because there are at most 26 characters.
+# Space Complexity: O(1) - `count` only stores counts for up to 26 characters.
+
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        # keep track of counts in the current window
+        count = {}
+        
+        left, right = 0, 0
+        res = 0
+        
+        # move the right pointer across the string
+        for right in range(len(s)):
+            # update the count for the character at the right pointer
+            count[s[right]] = count.get(s[right], 0) + 1
+
+            # if the window size minus the most frequent char count is bigger than k,
+            # need to shrink the window from the left
+            while (right - left + 1) - max(count.values()) > k:
+                # reduce the count of the char at the left pointer and move the left pointer
+                count[s[left]] -= 1
+                left += 1
+
+            # update the max length of the valid window
+            res = max(res, right - left + 1)
+
+        return res