<p>Given a string <code>s</code>, find <em>the longest palindromic <strong>subsequence</strong>&#39;s length in</em> <code>s</code>.</p>

<p>A <strong>subsequence</strong> is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;bbbab&quot;
<strong>Output:</strong> 4
<strong>Explanation:</strong> One possible longest palindromic subsequence is &quot;bbbb&quot;.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;cbbd&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> One possible longest palindromic subsequence is &quot;bb&quot;.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> consists only of lowercase English letters.</li>
</ul>

class Solution {
private:
    int solveSpaceOpt(string a, string b) {
        vector<int> curr(b.length() + 1, 0);
        vector<int> next(b.length() + 1, 0);

        for (int i = a.length() - 1; i >= 0; i--) {
            for (int j = b.length() - 1; j >= 0; j--) {
                int ans = 0;
                if (a[i] == b[j]) {
                    ans = 1 + next[j + 1];
                }
                else {
                    ans = max(next[j], curr[j + 1]);
                }
                curr[j] = ans;
            }
            next = curr;
        }
        return next[0];
    }

public:
    int longestPalindromeSubseq(string s) {
        string revStr = s;
        reverse(revStr.begin(), revStr.end());

        return solveSpaceOpt(s, revStr);
    }
};
8300