leetcode--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.public class Solution {
public boolean isPalindrome(String s) {
int low = 0;
int high = s.length()-1;
while(low<high){
if(!check(s.charAt(low))){
low++;continue;
}else if(!check(s.charAt(high))){
high--;continue;
}else{
if(s.charAt(low)!=s.charAt(high)&&s.charAt(low)-s.charAt(high)!=32
&& s.charAt(high)-s.charAt(low)!=32){
return false;
}else{
low++;high--;
}
}
}
return true;
}

public boolean check(char c){
if(c>='a'&&c<='z' || c>='A'&&c<='Z' || c>='0'&&c<='9')
return true;
return false;
}
}