题解 | #最长回文子串#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String a;
        try {
            a = in.readLine();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        char[] charAy = a.toCharArray();
        int i = 0, m, n, len, max = 0, l = charAy.length;
        for (; i < l - 1; i++) {
            len = 0;
            m = i;
            n = m + 1;
            while (m > -1 && n < l) {
                if (charAy[m] == charAy[n]) len += 2;
                else break;
                m--;
                n++;
            }
            max = max < len ? len : max;
        }
        i = 0;
        for (; i < l - 1; i++) {
            len = -1;
            m = i;
            n = m;
            while (m > -1 && n < l) {
                if (charAy[m] == charAy[n]) len += 2;
                else break;
                m--;
                n++;
            }
            max = max < len ? len : max;
        }
        System.out.print(max);
    }
}