题目来源：
https://leetcode-cn.com/problems/longest-palindromic-subsequence/
题目描述：
代码如下：
class Solution {
public int longestPalindromeSubseq(String s) {
if (s == null || s.length() == 0) return 0;
if(s.length()==1) return 1;
char[] chars = s.toCharArray();
if(s.length()==2) return chars[0] == chars[1] ? 2 : 1;
//三个字符才开始循环判断
int[][] array = new int[s.length()][s.length()];
for (int i = 0; i < s.length(); i++) {
array[i][i] = 1;
for (int j = i-1; j >-1 ; j--) {
if(chars[j]==chars[i]){
array[i][j] = 2 + array[i - 1][j + 1];
}else {
array[i][j] = Math.max(array[i-1][j],array[i][j+1]);
}
}
}
return array[chars.length-1][0];
}
}