[LeetCode] 1143. Longest Common Subsequence

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內容目錄

Medium

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.

Python

				
					# time complexity: O(n*m)
# space compleixty: O(n*m)
class Solution:
    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
        dpGrid = [[0] * (len(text2) + 1) for _ in range(len(text1)+1)]
        for col in reversed(range(len(text2))):
            for row in reversed(range(len(text1))):
                if text2[col] == text1[row]:
                    dpGrid[row][col] = 1 + dpGrid[row+1][col+1]
                else:
                    dpGrid[row][col] = max(
                        dpGrid[row+1][col], dpGrid[row][col+1])
        return dpGrid[0][0]


text1 = "abcde"
text2 = "ace"
print(Solution().longestCommonSubsequence(text1, text2))

Medium

Python

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