<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 {
public:
    int longestPalindromeSubseq(string s) {
        std::array<std::vector<int>, 2> v;
        v[0] = (std::vector(s.size() + 1, 0));
        v[1] = (std::vector(s.size() + 1, -1));
        for (int o = 0; o < s.size(); ++o) {
            for (int ii = 0; ii < s.size() - o; ++ii) {
                v[1][ii] = std::exchange(v[0][ii], std::max({v[0][ii], v[0][ii + 1], v[1][ii + 1] + 2 * static_cast<int>(s[ii] == s[ii + o])}));
            } 
        }

        return v[0][0];
    }
};
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