_516.java

package com.fishercoder.solutions;

/**
 * 516. Longest Palindromic Subsequence
 *
 * 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".
 */
public class _516 {

    /**Inspired by https://discuss.leetcode.com/topic/78603/straight-forward-java-dp-solution*/
    public static int longestPalindromeSubseq(String s) {
        int[][] dp = new int[s.length()][s.length()];
        for (int i = s.length()-1; i >= 0; i--) {
            dp[i][i] = 1;//initialization
            for (int j = i+1; j < s.length(); 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][s.length()-1];
    }

    public static void main(String... args) {
        longestPalindromeSubseq("bbbab");
        System.out.println("Done.");
    }

}