[freemjstudio] WEEK 08 Solutions

longest-repeating-character-replacement/freemjstudio.py

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+from collections import Counter
+
+# first solution -> O(N**2), time limit exceeded
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        max_length = 0
+
+        # window : length of the substring
+        for window in range(1, len(s)+1):
+            for i in range(len(s) - window + 1):
+                substring = s[i:i+window]
+
+                counter = Counter(substring)
+                max_count = max(counter.values())
+                if window - max_count <= k:
+                    max_length = max(max_length, window)
+
+        return max_length
+
+# second solution
+from collections import Counter
+
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        max_length = 0
+        counter = Counter()
+        left = 0
+
+        for right in range(len(s)):
+            counter[s[right]] += 1
+            max_count = max(counter.values())
+
+            window = right - left + 1
+            # window 사이즈가 조건에 맞도록 줄이기
+            while window - max_count > k:
+                counter[s[left]] -= 1
+                left += 1
+                max_count = max(counter.values())
+                window = right - left + 1 # update the window size because left has been moved
+
+            # 조건을 만족하는 window size 로 max length 를 갱신한다.
+            max_length = max(window, max_length)
+
+        return max_length

reverse-bits/freemjstudio.py

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+class Solution:
+    def reverseBits(self, n: int) -> int:
+        # 1. convert integer into binary
+        binary = bin(n)[2:]
+
+        # 2. convert into 32bits
+        fill_zero = 32 - len(binary)
+        binary = "0" * fill_zero + binary
+
+        # 3. reverse the binary
+        reversed_binary = binary[::-1]
+
+        # 4. convert binary into integer
+        return int(reversed_binary,2)