leetcode516 Longest Palindromic Subsequence

思路:

区间dp。

实现:

class Solution 
{
public:
    int longestPalindromeSubseq(string s) 
    {
        int n = s.length();
        int dp[1001][1001];
        for (int i = 0; i < n; i++)
        {
            dp[i][i] = 1;
            if (i != n - 1) dp[i][i + 1] = (s[i] == s[i + 1] ? 2 : 1);
        }
        for (int i = n - 1; i >= 0; i--)
        {
            for (int j = i + 2; j < n; j++)
            {
                if (s[i] == s[j]) dp[i][j] = dp[i + 1][j - 1] + 2;
                else dp[i][j] = max(dp[i + 1][j], dp[i][j - 1]);
            }
        }
        return dp[0][n - 1];
    }
};