#125 : Valid Palindrome solution

Author: heesun-task

valid-palindrome/heesun-task.py

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+# 125. Valid Palindrome 
+# Solution 1: Can early return False if chars don't match, so O(1) space.
+# Solution 2: Normalize the string first, then check if it's a palindrome. O(n) space for the normalized string.
+
+class Solution:
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
+    def isPalindrome(self, s: str) -> bool:
+        # Use two pointers from both ends
+        left, right = 0, len(s) - 1
+
+        # Move inward from both ends, ignore non-alphanumeric chars
+        # and compare chars case-insensitively. 
+        while left < right:
+            while left < right and not s[left].isalnum():
+                left += 1
+            while left < right and not s[right].isalnum():
+                right -= 1
+            if s[left].lower() != s[right].lower():
+                return False
+            left += 1
+            right -= 1
+        return True
+
+
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
+    def isPalindrome2(self, s:str) -> bool:
+        # Normalize the string by keeping only lowercase alphanumeric characters
+        s = list(filter(str.isalnum, s.lower()))
+        
+        # Check if the list is the same forwards and backwards 
+        return s == s[::-1]