Hello friends, 

 If you come here to check the solution of the following question. 

Longest Palindromic Substring in javascript

this question is asked in LeetCode as a Longest Palindromic Substring (Question Number -5) and its difficulty is medium.

So let's first understand the 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.

So the solution to the above question is.

/**
 * @param {string} s
 * @return {boolean}
 */
var longestPalindrome = function(s) {
    let startIndex = 0;
    let maxLength = 1;

    function expandMiddle(left, right) {
        while (left >= 0 && right < s.length && s[left] === s[right]) {
            const currentPalindromeLength = right - left + 1;
            if (currentPalindromeLength > maxLength) {
                maxLength = currentPalindromeLength;
                startIndex = left;
            }
            left -= 1;
            right += 1;
        }

    }
    for (let i = 0; i < s.length; i++) {
        expandMiddle(i - 1, i + 1);
        expandMiddle(i, i + 1)
    }
    return s.slice(startIndex,startIndex+maxLength)
    
};

The complexity of the solution is as follows:

Time Complexity: O(n²)- As expanding a palindrome around its center could take up to O(n) & we do this for each character.

Space Complexity: O(1)