Longest Palindromic Substring

Problem statement

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.

My solution

/**
 * @param {string} s
 * @return {string}
 */
var longestPalindrome = function(s) {
    let start = 0;
    let end = 0;
    
    function parse(left, right) {
        if (left > right || !s) {
            return 0;
        }
        
        while (left >= 0 && right < s.length && s.charAt(left) === s.charAt(right)) {
            left--
            right++
        }
        
        return right - left - 1;
    }
    
    
    for (let i = 0; i < s.length; i++) {
        const odd = parse(i, i);
        const even = parse(i, i + 1)
        
        const length = Math.max(odd, even);
        
        if (length > end - start) {
            start = Math.ceil(i - (length - 1)/2)
            end = i + length/2
        }
    }
    
    // console.log(start, end)
    
    return s.substring(start, end + 1)
};