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