add solution: longest-repeating-character-replacement

Author: dusunax

longest-repeating-character-replacement/dusunax.py

@@ -0,0 +1,32 @@
+'''
+# 424. Longest Repeating Character Replacement
+
+use sliding window to find the longest substring with at most k replacements.
+
+## Time and Space Complexity
+
+```
+TC: O(n)
+SC: O(1)
+```
+'''
+
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        freq = [0] * 26 # A~Z, SC: O(1)
+        left = 0
+        max_freq = 0
+        result = 0
+
+        for right in range(len(s)): # TC: O(n)
+            curr_char_index = ord(s[right]) - 65
+            freq[curr_char_index] += 1
+            max_freq = max(max_freq, freq[curr_char_index])
+            
+            if (right - left + 1) - max_freq > k:
+                freq[ord(s[left]) - 65] -= 1
+                left += 1
+
+            result = max(result, right - left + 1)
+
+        return result