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.

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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]