// TODO：write your code here
public String longestPalindrome(String s) {
        // TODO：write your code here
        return "";
    }
public String longestPalindrome(String s) {
// TODO：write your code here
return "";
}
public String longestPalindrome(String s) {
// TODO：write your code here
return "";
}
public String longestPalindrome(String s) {
// TODO：write your code here
return "";
}