[Leetcode 1143] Longest Common Subsequence

Problem link: https://leetcode.com/problems/longest-common-subsequence/?envType=problem-list-v2&envId=dynamic-programming

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.

Solution:

class Solution:
    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        dp = [[0 for j in range(len(text2) + 1)] for i in range(len(text1) + 1)]

        for i in range(len(text1) - 1, -1, -1):
            for j in range(len(text2) - 1, -1, -1):
                if text1[i] == text2[j]:
                    dp[i][j] = 1 + dp[i + 1][j + 1]
                else:
                    dp[i][j] = max(dp[i][j + 1], dp[i + 1][j])
        
        return dp[0][0]