leetcode 5. Longest Palindromic Substring

題目

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.


Example:


Input: "babad"


Output: "bab"


Note: "aba" is also a valid answer.
Example:


Input: "cbbd"


Output: "bb"

class Solution {
    private int start, maxLen;
    public String longestPalindrome(String s) {
        int n = s.length();
        if (n < 2) {
            return s;
        }
        for (int i = 0; i < n - 1; i++) {
            extendPalindrome(s, i, i);
            extendPalindrome(s, i, i + 1);
        }
        return s.substring(start, start + maxLen);
    }
    public void extendPalindrome(String s, int j, int k) {
        while (j >= 0 && k < s.length() && s.charAt(j) == s.charAt(k)) {
            j--;
            k++;
        }
        if (maxLen < k - j - 1) {
            start = j + 1;
            maxLen = k - j - 1;
        }
    }
}