516. Longest Palindromic Subsequence

Problem

Given a string s, find **the longest palindromic **subsequence's length in s.

A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

  Example 1:

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

Example 2:

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

  Constraints:

• 1 <= s.length <= 1000

• s consists only of lowercase English letters.

Solution (Java)

class Solution {
    public int longestPalindromeSubseq(String s) {
        char[] x = s.toCharArray();
        char[] y = new StringBuilder(s).reverse().toString().toCharArray();
        int m = x.length;
        int n = y.length;
        int[][] l = new int[m + 1][n + 1];
        for (int i = 0; i <= m; i++) {
            for (int j = 0; j <= n; j++) {
                if (i == 0 || j == 0) {
                    l[i][j] = 0;
                } else if (x[i - 1] == y[j - 1]) {
                    l[i][j] = l[i - 1][j - 1] + 1;

                } else {
                    l[i][j] = Math.max(l[i - 1][j], l[i][j - 1]);
                }
            }
        }
        return l[m][n];
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).