class Solution {
public:
int longestPalindromeSubseq(string s) {
int n = s.length();
vector<vector<int>> dp(n, vector<int>(n, 0));
// len = 1
for(int i = 0; i < n; ++i) {
dp[i][i] = 1;
}
for(int len = 2; len <= n; ++len) {
for(int i = 0; i + len <= n; ++i) {
int j = i + len - 1;
if(s[i] == s[j]) dp[i][j] = max(dp[i][j], dp[i+1][j-1] + 2);
else dp[i][j] = max(dp[i][j-1], dp[i+1][j]);
}
}
return dp[0][n-1];
}
};
// dp[i][j]: longest palindrome subsequence length within range i, j
// i j
// X X X X X [X X X X X] X X
