pylist

1143. Longest Common Subsequence

Given two strings text1 and text2, return the length of their longest common subsequence.

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. (eg, “ace” is a subsequence of “abcde” while “aec” is not). A common subsequence of two strings is a subsequence that is common to both strings.

If there is no common subsequence, return 0.

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 <= 1000
1 <= text2.length <= 1000
The input strings consist of lowercase English characters only.

Solution

from functools import lru_cache
class Solution:
    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        self.t1 = text1
        self.t2 = text2
        return self.dc(len(text1)-1, len(text2)-1)


    @lru_cache(None)
    def dc(self, i, j):
        if i < 0 or j < 0:
            return 0
        if self.t1[i] == self.t2[j]:
            return self.dc(i-1, j-1) + 1
        else:
            return max(self.dc(i, j-1), self.dc(i-1, j))

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