<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 dp[1001][1001];
    // int solve(int ind1,int ind2,string &s, string &t){
    //     if(ind1<0 || ind2<0) return 0;
    //     if(s[ind1]==t[ind2]) return 1+solve(ind1-1,ind2-1,s,t);
    //     if(dp[ind1][ind2]!=-1) return dp[ind1][ind2];
    //     return dp[ind1][ind2]=max(solve(ind1-1,ind2,s,t),solve(ind1,ind2-1,s,t));
    // }
    int longestPalindromeSubseq(string s) {
        int n=s.size();
        string t=s;
        reverse(t.begin(),t.end());
        memset(dp,0,sizeof(dp));
       vector<int>prev(n+1,0);
       vector<int>curr(n+1,0);
       for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(s[i-1]==t[j-1]) curr[j]=1+prev[j-1];
            else curr[j]=max(prev[j],curr[j-1]);
        }
        prev=curr;
       }
      
       return prev[n];
    }
};
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