Valid Palindrome 415
Question
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Notice
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.
Example
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.
Challenge
O(n) time without extra memory.
Solution
前后指针,用Character.isLetterOrDigit来判断是否是字符和数字。
代码如下:
public class Solution {
/**
* @param s A string
* @return Whether the string is a valid palindrome
*/
public boolean isPalindrome(String s) {
// Write your code here
if(s == null){
return false;
}
if(s.length() == 0){
return true;
}
s = s.toLowerCase();
for(int i = 0, j = s.length() - 1; i < j; i++, j--){
while(i < j && !Character.isLetterOrDigit(s.charAt(i))){
i++;
}
while(i < j && !Character.isLetterOrDigit(s.charAt(j))){
j--;
}
if(s.charAt(i) != s.charAt(j)){
return false;
}
}
return true;
}
}