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Longest Palindromic Substring

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Write a JavaScript program to find the longest palindromic substring in a given string. A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward. For example, "racecar" is a palindrome because it reads the same in both directions.

Example 1
    
  
  • Input: s = "babad"
    • 
  
  • Output: "bab"
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  • Explanation: 
    • The string "babad" contains multiple palindromic substrings. 
    • We can find "bab" starting at index 0, which has length 3. 
    • We can also find "aba" starting at index 1, which also has length 3. 
    • Both are valid answers since they have the same maximum length.
    •
Example 2
    
  
  • Input: s = "cbbd"
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  • Output: "bb"
    • 
  
  • Explanation: 
    • The string "cbbd" is analyzed for palindromic substrings. 
    • Individual characters 'c', 'b', 'b', 'd' are palindromes of length 1. 
    • The substring "bb" at indices 1-2 is a palindrome of length 2. 
    • "bb" is the longest palindromic substring in this case.
    •
Constraints
    
  
  • 1 ≤ s.length ≤ 1000
    • 
  
  • s consists of only lowercase English letters
    • 
  
  • Time Complexity: O(n^2)
    • 
  
  • Space Complexity: O(1)
    •
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Hint
Solution

Solution Hints

    
  
  • Use the "expand around centers" approach to check for palindromes
    • 
  
  • For each character, treat it as a potential center of a palindrome
    • 
  
  • Expand outward from each center while characters match
    • 
  
  • Handle both odd-length and even-length palindromes separately
    • 
  
  • Keep track of the longest palindrome found so far
    •

Steps to solve by this approach:

 Step 1: Initialize variables to track the starting position and maximum length of the longest palindrome found.

 Step 2: Create a helper function that expands around a given center to find palindromes.

 Step 3: For each position in the string, use it as a center for odd-length palindromes.

 Step 4: For each position in the string, use it and the next position as centers for even-length palindromes.

 Step 5: In the expand function, move outward while characters match and update the longest palindrome if a longer one is found.

 Step 6: Continue until all possible centers have been checked.

 Step 7: Return the substring using the recorded start position and maximum length.

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