[5. Longest Palindromic Substring] #leetcode

5_0914.java

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

        int start = 0;
        int end = 0;

        // foreach find longest
        for (int i = 0; i < s.length(); i++) {
            int p1 = findPalindrome(s, i, i);
            int p2 = findPalindrome(s, i, i + 1);
            int maxLen = Math.max(p1, p2);
            if (maxLen > end - start) {
                start = i - (maxLen - 1) / 2;
                end = i + maxLen / 2 + 1;
            }
        }

        // output
        return s.substring(start, end);
    }

    private static int findPalindrome(String s, int left, int right) {
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
            // check left and right
            left--;
            right++;
        }
        return right - left - 1;
    }
}