# 1143 Longest Common Subsequence

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.
 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 `````` ``````class Solution: def longestCommonSubsequence(self, text1: str, text2: str) -> int: m, n = len(text1)+1, len(text2)+1 dp = [[0] * n for _ in range(2)] for i in range(1, m): ri = i % 2 pi = (i - 1) % 2 for j in range(1, n): if text1[i-1] == text2[j-1]: dp[ri][j] = 1 + dp[pi][j-1] else: dp[ri][j] = max(dp[pi][j], dp[ri][j-1]) return dp[(m-1) % 2][-1]``````