Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Input: "cbbd"
Output: "bb"
class Solution {
public String longestPalindrome(String s) {
int n = s.length();
String res = null;
boolean[][] dp = new boolean[n][n];
for (int j = 0; j < n; j++) {
for (int i = j; i >= 0; i--) {
if (s.charAt(i) == s.charAt(j) && (j - i <= 2 || dp[i + 1][j - 1])) {
dp[i][j] = true;
}
if (dp[i][j] && (res == null || j - i + 1 > res.length())) {
res = s.substring(i, j + 1);
}
}
}
return res;
}
}