longest palindromic subsequence

Leetcode 516. Longest Palindromic Subsequence

Solution: dynamic programming method

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