English
516. Longest Palindromic Subsequence 
Problem Statement:
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
public int longestPalindromeSubseq(String s) {
String str1 = s,
str2 = new StringBuilder(s).reverse().toString();
int m = str1.length(),
n = str2.length();
int[][] dp = new int[m + 1][n + 1];
for (int i = 0; i < m + 1; i++)
for (int j = 0; j < n + 1; j++) {
if (i == 0 || j == 0)
dp[i][j] = 0;
else if (str1.charAt(i - 1) == str2.charAt(j - 1))
dp[i][j] = 1 + dp[i - 1][j - 1];
else
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
}
return dp[m][n];
}
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