class Solution {
public String longestPalindrome(String s) {
if(s == null || s.equals("")){
return s;
}
int n = s.length();
boolean[][] dp = new boolean[n][n];
int begin = 0;
int len = 1;
//base
for(int i = 0;i < n;i++){
dp[i][i] = true;
}
//状态转移
for(int i = n-1;i>=0;i--){
for(int j =i+1;j<n;j++){
if(s.charAt(i)==s.charAt(j)){
if(j - i < 3){
dp[i][j] = true;
}
else{
dp[i][j] = dp[i+1][j-1];
}
}
else{
dp[i][j] = false;
}
if(dp[i][j] == true && j-i+1>len){
begin = i;
len = j-i+1;
}
}
}
return s.substring(begin,begin+len);
}
}
