<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 solve(int i1,int i2,string &t1,string &t2,vector<vector<int>>&dp){
    // if(i1==0 && i2==0) return (t1[i1]==t2[i2]);
    if(i1<0 || i2<0) return 0;
    if(dp[i1][i2]!=-1) return dp[i1][i2];
    if(t1[i1]==t2[i2]){
        return dp[i1][i2]=1+solve(i1-1,i2-1,t1,t2,dp);
    }
    else{
        return dp[i1][i2]=max(solve(i1-1,i2,t1,t2,dp),solve(i1,i2-1,t1,t2,dp));
        
    }

}
    int longestPalindromeSubseq(string t1) {
        string t2=t1;
        reverse(t2.begin(),t2.end());
        int n=t1.size();
        int m=t2.size();
        vector<int>prev(m+1, 0);
        for(int i1=1;i1<=n;i1++){
            vector<int>curr(m+1, 0);
            for(int i2=1;i2<=m;i2++){
                if(t1[i1-1]==t2[i2-1]){
        curr[i2]=1+prev[i2-1];
    }
    else{
        curr[i2]=max(prev[i2],curr[i2-1]);
        
    }
            }
            prev=curr;
        }
        return prev[m];
    }
};
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