1143_Longest_Common_Subsequence.md

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.

def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        size1 = len(text1)
        size2 = len(text2)
        
        dp = [[0] * (size2+1) for _ in range(size1+1)]
        
        # print(dp)
        
        for i in range(1, size1+1):
            for j in range(1, size2+1):
                
                if text1[i-1] == text2[j-1]:
                    dp[i][j] = dp[i-1][j-1]+1
                else:
                    dp[i][j] = max(dp[i-1][j], dp[i][j-1], dp[i-1][j-1])
                    
        return dp[-1][-1]

Runtime: 476 ms, faster than 38.20% of Python3 online submissions for Longest Common Subsequence.
Memory Usage: 21.9 MB, less than 78.67% of Python3 online submissions for Longest Common Subsequence.