Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
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.
Solution
(Valid-Palindrome.py) download
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| class Solution(object):
def isPalindrome(self, s):
"""
:type s: str
:rtype: bool
"""
if not s:
return True
s = s.lower()
l = 0
r = len(s)-1
alpha = "0123456789abcdefghijklmnopqrstuvwxyz"
while l<r:
while l < r and s[l] not in alpha:
l += 1
if l >= r:
return True
while l<r and s[r] not in alpha:
r -= 1
if l == r:
return True
if s[l] != s[r]:
return False
l += 1
r -= 1
return True
|
(Valid-Palindrome.java) download
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| public class Solution {
public boolean isPalindrome(String s) {
if (s == null)
return true;
int l = 0;
int r = s.length()-1;
while (l < r){
while ((l < r) && !(Character.isLetterOrDigit(s.charAt(l))))
l += 1;
while ((l < r) && !(Character.isLetterOrDigit(s.charAt(r))))
r -= 1;
if (Character.toLowerCase(s.charAt(l)) != Character.toLowerCase(s.charAt(r)))
return false;
l += 1;
r -= 1;
}
return true;
}
}
|