Shortest Palindrome leetcode-java

public class Solution {
public String shortestPalindrome(String s) {
if(s.length() == 0||s.length() == 1)
return s;
String mirror = s + new StringBuilder(s).reverse().toString()+" ";
int[] next = new int[mirror.length()];
int i=0;
int j=-1;
next[0]=-1;
while(i<mirror.length()-1){
if(j==-1||mirror.charAt(i)==mirror.charAt(j)){
i++;
j++;
next[i]=j;
}else j=next[j];
}
int count = s.length() - next[mirror.length() -1];
if(count<0)count =0;
String result = new StringBuilder(s.substring(s.length()-count, s.length())).reverse().toString() + s;
return result;
}
}