<p>Given two strings <code>text1</code> and <code>text2</code>, return <em>the length of their longest <strong>common subsequence</strong>. </em>If there is no <strong>common subsequence</strong>, return <code>0</code>.</p>

<p>A <strong>subsequence</strong> of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.</p>

<ul>
	<li>For example, <code>&quot;ace&quot;</code> is a subsequence of <code>&quot;abcde&quot;</code>.</li>
</ul>

<p>A <strong>common subsequence</strong> of two strings is a subsequence that is common to both strings.</p>

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

<pre>
<strong>Input:</strong> text1 = &quot;abcde&quot;, text2 = &quot;ace&quot; 
<strong>Output:</strong> 3  
<strong>Explanation:</strong> The longest common subsequence is &quot;ace&quot; and its length is 3.
</pre>

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

<pre>
<strong>Input:</strong> text1 = &quot;abc&quot;, text2 = &quot;abc&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> The longest common subsequence is &quot;abc&quot; and its length is 3.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> text1 = &quot;abc&quot;, text2 = &quot;def&quot;
<strong>Output:</strong> 0
<strong>Explanation:</strong> There is no such common subsequence, so the result is 0.
</pre>

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

<ul>
	<li><code>1 &lt;= text1.length, text2.length &lt;= 1000</code></li>
	<li><code>text1</code> and <code>text2</code> consist of only lowercase English characters.</li>
</ul>

class Solution {
private:
int dp(int ind1, int ind2, string &t1, string &t2, vector<vector<int>> &cache) {
    if (ind1 < 0 || ind2 < 0) {
        return 0;
    }
    if (cache[ind1][ind2] != -1) {
        return cache[ind1][ind2];
    }

    if (t1[ind1] == t2[ind2]) {
        cache[ind1][ind2] = 1 + dp(ind1-1, ind2-1, t1, t2, cache);
    } else {
        cache[ind1][ind2] = max (dp(ind1-1, ind2, t1, t2, cache), dp(ind1, ind2-1, t1, t2, cache));
    }
    return cache[ind1][ind2];
}


public:
    int longestCommonSubsequence(string text1, string text2) {
        vector<vector<int>> cache(text1.size(), vector<int>(text2.size(), -1));
        return dp(text1.size()-1, text2.size()-1, text1, text2, cache);
    }
};
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