# 516. Longest Palindromic Subsequence

## 1. Question

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.

## 2. Examples

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".


## 3. Constraints

• 1 <= s.length <= 1000
• s consists only of lowercase English letters.

## 5. Solutions

class Solution {
public int longestPalindromeSubseq(String s) {
int n = s.length();
int[][] dp = new int[n][n];
for (int i = n - 1; i >= 0; i--) {
dp[i][i] = 1;
char c1 = s.charAt(i);
for (int j = i + 1; j < n; j++) {
char c2 = s.charAt(j);
if (c1 == c2) {
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[n - 1];
}
}

// 解答来源于官方 本菜鸡不会