Problem
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.
My Solution
class Solution {
public boolean isPalindrome(String s) {
if (s.isEmpty()) {
return true;
}
int head = 0, tail = s.length() - 1;
char cHead, cTail;
while (head <= tail) {
cHead = s.charAt(head);
cTail = s.charAt(tail);
if (!Character.isLetterOrDigit(cHead)) {
head++;
} else if (!Character.isLetterOrDigit(cTail)) {
tail--;
} else {
if (Character.toLowerCase(cHead) != Character.toLowerCase(cTail)) {
return false;
}
head++;
tail--;
}
}
return true;
}
}
Great Solution
public boolean isPalindrome(String s) {
String actual = s.replaceAll("[^A-Za-z0-9]", "").toLowerCase();
String rev = new StringBuffer(actual).reverse().toString();
return actual.equals(rev);
}
