Longest Palindromic Subsequence

题目
Given a string s, find the longest palindromic subsequence's length in s. You may assume that the maximum length of s is 1000.

Example 1:

Input:
"bbbab"
Output:
4
One possible longest palindromic subsequence is "bbbb".

Example 2:

Input:
"cbbd"
Output:
2
One possible longest palindromic subsequence is "bb".

答案

class Solution {
    public int longestPalindromeSubseq(String s) {
        int [][] lps = new int[s.length()][s.length()]; 
        for(int i = s.length() - 1; i >= 0; i--) {
            for(int j = i; j < s.length(); j++) {
                if(i == j)
                    lps[i][j] = 1;
                else if(j == i + 1)
                    lps[i][j] = (s.charAt(i) == s.charAt(j))?2:1;
                else {
                    if(s.charAt(i) == s.charAt(j))
                        lps[i][j] = lps[i + 1][j - 1] + 2;
                    else
                        lps[i][j] = Math.max(lps[i + 1][j -1], Math.max(lps[i][j - 1], lps[i + 1][j]));
                }
            }
        }
        return lps[0][s.length() - 1];
    }
}