[Solved] Given a string s, find the longest palindromic subsequence’s length in s. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

Question

Given a string s, find the longest palindromic subsequence‘s length in s.

subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

Example 1:

Input: s = "bbbab"
Output: 4
Explanation: One possible longest palindromic subsequence is "bbbb".

Example 2:

Input: s = "cbbd"
Output: 2
Explanation: One possible longest palindromic subsequence is "bb".

Constraints:

  • 1 <= s.length <= 1000
  • s consists only of lowercase English letters.

Python Solution

class Solution:
    def longestPalindromeSubseq(self, s: str) -> int:
        l = len(s)
        matrix = [[0 for _ in range(l)] for _ in range(l)]
        
        for i in range(l):
            matrix[i][i] = 1
        
        for i in range(l-1,-1,-1):
            for j in range(i+1,l):
                if s[i]==s[j]:
                    matrix[i][j] = matrix[i+1][j-1] + 2
                else:
                    matrix[i][j] = max(matrix[i+1][j],matrix[i][j-1])
        
        return matrix[0][-1]
Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

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