# 1143. Longest Common Subsequence

#### Medium

***

Given two strings `text1` and `text2`, return *the length of their longest **common subsequence**.* If there is no **common subsequence**, return `0`.

A **subsequence** 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.

* For example, `"ace"` is a subsequence of `"abcde"`.

A **common subsequence** of two strings is a subsequence that is common to both strings.

 

**Example 1:**

```
Input: text1 = "abcde", text2 = "ace" 
Output: 3  
Explanation: The longest common subsequence is "ace" and its length is 3.
```

**Example 2:**

```
Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.
```

**Example 3:**

```
Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0.
```

 

**Constraints:**

* `1 <= text1.length, text2.length <= 1000`
* `text1` and `text2` consist of only lowercase English characters.

```python
class Solution:
    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        m = len(text1)
        n = len(text2)
        arr = [[0 for j in range(n+1)] for i in range(m+1)]
        for i in range(1, m+1):
            for j in range(1, n+1):
                if text1[i-1] == text2[j-1]:
                    arr[i][j] = 1 + arr[i-1][j-1]
                else:
                    arr[i][j] = max(arr[i-1][j], arr[i][j-1])
        return arr[m][n]
```