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.
解题思路：
注意题目，忽略大小写，忽略非字母或数字，JAVA实现如下：
public boolean isPalindrome(String s) {
if(s.length()<=1)
return true;
int left=0,right=s.length()-1;
while(left<right){
if(!Character.isLetterOrDigit(s.charAt(left))){
left++;
continue;
}
if(!Character.isLetterOrDigit(s.charAt(right))){
right--;
continue;
}
if(Character.toUpperCase(s.charAt(left))!=Character.toUpperCase(s.charAt(right)))
return false;
left++;
right--;
}
return true;
}