Longest Palindromic Subsequence

Question

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".

Tags

• Array

Thought

Reference: http://bookshadow.com/weblog/2017/02/12/leetcode-longest-palindromic-subsequence/

Use the dynamic programming to record the count.

Code

public class Solution {
    public int longestPalindromeSubseq(String s) {
        int size = s.length();
        int[][] dp = new int[size][size];
        for (int i = size - 1; i >= 0; i--) {
            dp[i][i] = 1;
            for (int j = i + 1; j < size; 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][size - 1];
    }
}