516. Longest Palindromic Subsequ

https://leetcode.com/problems/longest-palindromic-subsequence/description/
解题思路：

1. 判断sequence两端是否相等，如相等 dp[i][j] = dp[i+1][j-1] + 2；如不相等：dp[i][j] =
   Math.max(dp[i - 1][j], dp[i][j - 1]);

代码如下：
class Solution {
public int longestPalindromeSubseq(String s) {

    int len = s.length();
    int[][] dp = new int[len][len];
    for(int i = len - 1; i >= 0; i--){
        dp[i][i] = 1;
        for(int j = i + 1; j < len; j++){
            if(s.charAt(i) == s.charAt(j)){
                dp[i][j] = dp[i + 1][j - 1] + 2;
            } else{
                dp[i][j] = Math.max(dp[i + 1][j], dp[i][j - 1]);
            }
        }
    }
    return dp[0][len - 1];
}

}