<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 f(int ind1, int ind2, string s, string t)
    {
        if(ind1 < 0 or ind2 < 0)return 0;
        if(s[ind1] == t[ind2])return 1 + f(ind1-1, ind2-1, s, t);
        return max(f(ind1-1,ind2,s,t),f(ind1,ind2-1,s,t));
    }
    int longestPalindromeSubseq(string s) {
        string t = s;
        reverse(t.begin(),t.end());
        // return f(s.size()-1, s.size()-1,s,t);
        int n = s.size();
        vector<int> prev(n+1,0), curr(n+1,0);
        // vector<vector<int>> dp(n+1,vector<int>(n+1,0));
        for(int ind1 = 1; ind1 <= n; ind1++)
        {
            for(int ind2 = 1; ind2 <= n; ind2++)
            {
                if(s[ind1-1] == t[ind2-1])curr[ind2] = 1 + prev[ind2-1];
                else curr[ind2] = max(prev[ind2],curr[ind2-1]);
            }
            prev = curr;
        }
        return prev[n];
    }
};
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