一、题目

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.

二、题解

class Solution {
public:int longestPalindromeSubseq(string s) {string s1 = s;reverse(s1.begin(),s1.end());int n = s.size();vector<vector<int>> dp(n+1,vector<int>(n+1,0));for(int i = 1;i <= n;i++){for(int j = 1;j <= n;j++){if(s[i-1] == s1[j-1]) dp[i][j] = 1 + dp[i-1][j-1];else dp[i][j] = max(dp[i-1][j],dp[i][j-1]);}}return dp[n][n];}
};