valid palindrome solution refactor

Author: jylee2033

valid-palindrome/jylee2033.py

@@ -3,12 +3,31 @@ def isPalindrome(self, s: str) -> bool:
         # 1. Remove non-alphanumeric characters and convert to lowercase
         # 2. Compare with reversed string
 
-        cleaned_s = ""
-        for ch in s:
-            if ch.isalnum():
-                cleaned_s += ch.lower()
+        # cleaned_s = ""
+        # for ch in s:
+        #     if ch.isalnum():
+        #         cleaned_s += ch.lower()
 
-        return cleaned_s == cleaned_s[::-1]
+        # return cleaned_s == cleaned_s[::-1]
 
 # Time Complexity : O(n)
 # Space Complexity : O(n)
+
+        left = 0
+        right = len(s) - 1
+
+        while left < right:
+            if not s[left].isalnum():
+                left += 1
+            elif not s[right].isalnum():
+                right -= 1
+            elif s[left].lower() != s[right].lower():
+                return False
+            else:
+                left += 1
+                right -= 1
+
+        return True
+
+# Time Complexity : O(n)
+# Space Complexity : O(1)