LeetCode

Question 1

Longest Palindromic Substring (Medium)

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.

Answer 1

public class Solution {
    public String longestPalindrome(String s) {
        if (s.length() <= 1) {
            return s;
        }

        String maxStr = s.substring(0, 1);

        for (int i = 0; i < s.length() - 1; i++) {
            String odd = expandFromCenter(s, i, i);
            String even = expandFromCenter(s, i, i + 1);

            if (odd.length() > maxStr.length()) {
                maxStr = odd;
            }
            if (even.length() > maxStr.length()) {
                maxStr = even;
            }
        }

        return maxStr;
    }

    private String expandFromCenter(String s, int left, int right) {
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
            left--;
            right++;
        }
        return s.substring(left + 1, right);
    }
}