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.
Solution：Check by two pointers from head&end
skip non-alphanumeric before checking
Time Complexity: O(N) Space Complexity: O(1)
Solution Code：
class Solution {
public boolean isPalindrome(String s) {
if(s == null || s.isEmpty()) return true;
int start = 0, end = s.length() - 1;
while(start < end) {
while(start < end && !Character.isLetterOrDigit(s.charAt(start))) start++;
while(start < end && !Character.isLetterOrDigit(s.charAt(end))) end--;
if(Character.toLowerCase(s.charAt(start)) == Character.toLowerCase(s.charAt(end))) {
start++;
end--;
}
else {
return false;
}
}
return true;
}
}
