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125-valid_palindrome.py
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125-valid_palindrome.py
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"""
https://leetcode.com/problems/valid-palindrome/
A phrase is a palindrome if, after converting all uppercase letters into
lowercase letters and removing all non-alphanumeric characters, it reads
the same forward and backward. Alphanumeric characters include letters
and numbers.
Given a string s, return true if it is a palindrome, or false otherwise.
Example 1:
Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.
Example 2:
Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.
Example 3:
Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.
Constraints:
1 <= s.length <= 2 * 10^5
s consists only of printable ASCII characters.
"""
def isPalindrome(s: str) -> bool:
s = ''.join(c.lower() for c in s if c.isalnum())
left = 0
right = len(s) - 1
while left < right:
if s[left] != s[right]:
return False
left += 1
right -= 1
return True
if __name__ == '__main__':
s = "A man, a plan, a canal: Panama"
print(isPalindrome(s))