leetcode LongestPalindromicSubstring

public class LongestPalindromicSubstring {
  public String longestPalindrome(String s) {
    String ans = "";
    boolean[][] dp = new boolean[s.length()][s.length()];
    for (int j=0; j<s.length(); j++) {
      for (int i=0; i<=j; i++) {
        if (((j>i+1 && dp[i+1][j-1]) || j <= i+1 ) && s.charAt(i) == s.charAt(j)) {
          dp[i][j] = true;
          if (j-i+1 > ans.length()) {
            ans = s.substring(i, j+1);
          }
        }
      }
    }
    return ans;
  }


  public boolean isPalindrome(String s, int i, int j) {
    int left = i;
    int right = j;
    while (left < right) {
      if (s.charAt(left) != s.charAt(right) ){
        return false;
      }
      left ++;
      right --;
    }
    return true;
  }
}