Longest Palindromic Substring | Leetcode

Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

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Solution: For each index in the string, find the longest palindrome that centers in that index. Note that a palindrome with an odd length and one with an even length have to be checked for separately. Return the longest palindrome ever found.

public class Solution {
    public String longestPalindrome(String s) {
        if (s.length() <= 1) return s;
        
        int maxLength = 0;
        int maxStart = 0;
        int maxEnd = 0;
        
        for (int i = 0, last = s.length() - 1; i <= last; i++) {
            // Find longest palindrome with odd number of characters.
            int start = i;
            int end = i;
            while (start > 0 && end < last && s.charAt(start - 1) == s.charAt(end + 1)) {
                start--;
                end++;
            }
            if (end - start + 1 > maxLength) {
                maxLength = end - start + 1;
                maxStart = start;
                maxEnd = end;
            }
            
            // Find longest palindrome with even number of characters.
            start = i + 1;
            end = i;
            while (start > 0 && end < last && s.charAt(start - 1) == s.charAt(end + 1)) {
                start--;
                end++;
            }
            if (end - start + 1 > maxLength) {
                maxLength = end - start + 1;
                maxStart = start;
                maxEnd = end;
            }
        }
        
        return s.substring(maxStart, maxEnd + 1);
    }
}