<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>

import functools

class Solution:
    @functools.lru_cache(maxsize=10000)
    def helper(self, s1, s2, i, j):
        if i < 0 or j < 0:
            return 0
        if s1[i] == s2[j]:
            res = 1 + self.helper(s1,s2,i-1,j-1)
        else:
            res = max(self.helper(s1,s2,i,j-1), self.helper(s1,s2,i-1,j))
        return res
    # def helper(self, s1, s2, i, j):
    #     if i < 0 or j < 0:
    #         return 0
    #     if (i,j) in self.cache:
    #         return self.cache[(i,j)]
    #     if s1[i] == s2[j]:
    #         res = 1 + self.helper(s1,s2,i-1,j-1)
    #     else:
    #         res = max(self.helper(s1,s2,i,j-1), self.helper(s1,s2,i-1,j))
    #     self.cache[(i,j)] = res
    #     return res
        

    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        return self.helper(text1, text2, len(text1)-1, len(text2)-1)
21716