6.5

epi_judge_python/is_string_palindromic_punctuation.py

@@ -1,13 +1,46 @@
 from test_framework import generic_test
 
 
+# O(n) time complexity O(1) space
+def is_palindrome(s: str):
+    i = 0
+    j = len(s) - 1
+    trip = True if s == "" else False
+    while i < j:
+        if not s[i].isalnum():
+            i += 1
+        elif not s[j].isalnum():
+            j -= 1
+        elif s[i].lower() == s[j].lower():
+            trip = True
+            i += 1
+            j -= 1
+        else:
+            return False
+    return trip
+
+
+# solution from book
 def is_palindrome(s):
-    # TODO - you fill in here.
+    # i moves forward, and j moves backward.
+    i, j = 0, len(s) - 1
+    while i < j:
+        # i and j both skip non-alphanumeric characters.
+        while not s[i].isalnum() and i < j:
+            i += 1
+        while not s[j].isalnum() and i < j:
+            j -= 1
+        if s[i].lower() != s[j].lower():
+            return False
+        i, j = i + 1, j - 1
     return True
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     exit(
-        generic_test.generic_test_main("is_string_palindromic_punctuation.py",
-                                       "is_string_palindromic_punctuation.tsv",
-                                       is_palindrome))
+        generic_test.generic_test_main(
+            "is_string_palindromic_punctuation.py",
+            "is_string_palindromic_punctuation.tsv",
+            is_palindrome,
+        )
+    )