leetcode - 5.Longest Palindromic Substring

Longest Palindromic Substring

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

Example1:

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Example2:

Input: "cbbd"

Output: "bb"

Solution:

  private int start = 0;
    private int end = 0;

    public String longestPalindrome(String s) {
        int length = s.length();
        if (length < 2) {
            return s;
        }

        for (int i = 0; i < length; i++) {
            // 奇
            searchPalindrome(s, i, i);
            // 偶
            searchPalindrome(s, i, i + 1);
        }

        return s.substring(start, end);
    }

    private void searchPalindrome(String s, int x, int y) {
        int length = s.length();
        while (x > -1 && y < length && s.charAt(x) == s.charAt(y)) {
            x--;
            y++;
        }

        if (y - x > end - start + 1) {
            start = x + 1;
            end = y;
        }
    }