[Solved] Given a string s, return the longest palindromic substring in s.

Question

Given a string s, return the longest palindromic substring in s.

Example 1:

Input: s = "babad"
Output: "bab"
Explanation: "aba" is also a valid answer.

Example 2:

Input: s = "cbbd"
Output: "bb"

Constraints:

  • 1 <= s.length <= 1000
  • s consist of only digits and English letters.

Python Solution

class Solution:
    def longestPalindrome(self, s: str) -> str:
        start = 0
        max_len = 1
        l = len(s)
        
        dp_matrix = [[0 for i in range (l)] for j in range (l)]
        
        # diagonal single characters
        for i in range(l):
            dp_matrix[i][i] = 1
        
        # two characters like ba, ab, ba, ad
        for i in range (l-1):
            if s[i]==s[i+1]:
                dp_matrix[i][i+1] = 1
                max_len = 2
                start = i
        
        # general case for strings of len>=3
        k=3
        while k<=l:
            for i in range(l-k+1):
                j=i+k-1
                if s[i]==s[j] and dp_matrix[i+1][j-1]:
                    dp_matrix[i][j] = 1
                    if k>max_len:
                        max_len = k
                        start = i
            k+=1
        return s[start:start+max_len]
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.

Articles: 520

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