[ppxyn1] WEEK 08 solutions

longest-common-subsequence/ppxyn1.py

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+# idea : recursive 
+# Time complexity : O(len(text1)*len(text2))
+
+class Solution:
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+        @cache
+        def dfs(i, j):
+            if i == len(text1) or j == len(text2):
+                return 0
+            if text1[i] == text2[j]:
+                match_len = 1 + dfs(i+1, j+1)
+                return match_len
+            else:
+                return max(dfs(i + 1, j), dfs(i, j + 1))
+        return dfs(0, 0)
+
+
+

palindromic-substrings/ppxyn1.py

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+# idea : palindrome
+# Time Complexity: O(n^2)
+
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        result = 0
+
+        for i in range(len(s)):            
+            # odd 
+            left = i
+            right = i
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                result += 1
+                left -= 1
+                right += 1
+
+            # even
+            left = i
+            right = i + 1
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                result += 1
+                left -= 1
+                right += 1
+
+        return result
+
+
+

reverse-bits/ppxyn1.py

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+# idea: -
+# Time Complexity : O(1) since just fixed 32bit 
+
+class Solution:
+    def reverseBits(self, n: int) -> int:
+        bits = bin(n)[2:]              
+        bits = bits.zfill(32)          # 32bits
+        reversed_bits = bits[::-1]     
+        return int(reversed_bits, 2)   # binary to int 
+