Valid Palindrome

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.

写一个方法判断是否为正确的字母，然后start＋＋，end－－。

package leetcode;

public class ValidPalindrome {
public boolean isPalindrome(String
s) {
if (s.equals(""))
return
true;
s =
s.toLowerCase();
int
len = s.length();
int
left = 0, right = len - 1;
while (left <
right) {
while (!isValid(s.charAt(left))) {
left++;
if (left >=
right)
return
true;
}
while (!isValid(s.charAt(right))) {
right--;
if (left >=
right)
return
true;
}
//System.out.println(s.charAt(left) + " " + s.charAt(right));
if (s.charAt(left) !=
s.charAt(right))
return
false;
left++;
right--;
}
return
true;
}

private boolean isValid(char
charAt) {
if ('a' <=
charAt && charAt <=
'z')
return
true;
if ('0' <=
charAt && charAt <=
'9')
return
true;
return
false;
}

public static
void main(String[] args) {
//
TODO Auto-generated method stub
System.out.println(new ValidPalindrome().isPalindrome("a."));
System.out.println(new ValidPalindrome().isValid('.'));
}

}