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125_Valid_Palindrome.py
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125_Valid_Palindrome.py
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# Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
#
# For example,
# "A man, a plan, a canal: Panama" is a palindrome.
# "race a car" is not a palindrome.
#
# Note:
# Have you consider that the string might be empty? This is a good question to ask during an interview.
#
# For the purpose of this problem, we define empty string as valid palindrome.
#
# Tags: Two Pointers, String
# Difficulty: Easy
class Solution(object):
def isPalindrome(self, s):
"""
:type s: str
:rtype: bool
"""
valid_chars = set('0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz')
i, j = 0, len(s) - 1
while i < j:
if s[i] not in valid_chars:
i += 1
continue
if s[j] not in valid_chars:
j -= 1
continue
if s[i].lower() == s[j].lower():
i += 1
j -= 1
else:
return False
return True