Longest Palindromic Substring--leetcode

常规算法（效率较低）：

public static String longestPalindrome(String s) {
int num = 0;
String result = "";
for(int i = 0;i < s.length();i++){
for(int j = i + 1;j <= s.length();j++){
if(isPalindrome(s.substring(i, j))){
if(j-i > num){
num = j-i;
result = s.substring(i, j);
}
}
}
}
return result;
}
public static Boolean isPalindrome(String s){
StringBuilder strB = new StringBuilder(s);
strB.reverse();
String str = new String(strB);
if(str.equals(s)){
return true;
}else{
return false;
}
}