LeetCode 516. Longest Palindromic Subsequence

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”.

分析

按长度来更新dp数组，
if(s[j]==s[j+len-1])
dp[j][j+len-1]=dp[j+1][j+len-2]+2;
else
dp[j][j+len-1]=max(dp[j+1][j+len-1],dp[j][j+len-2]);

class Solution {
public:
    int longestPalindromeSubseq(string s) {
        vector<vector<int>> dp(s.size(),vector<int>(s.size(),0));
        for(int i=0;i<s.size();i++)
            dp[i][i]=1;
        for(int len=2;len<=s.size();len++)
            for(int j=0;j<=s.size()-len;j++)
                if(s[j]==s[j+len-1])
                   dp[j][j+len-1]=dp[j+1][j+len-2]+2;
                else
                   dp[j][j+len-1]=max(dp[j+1][j+len-1],dp[j][j+len-2]);
       return dp[0][s.size()-1];
    }
};