题解 | #密码截取#

实际上就是最长回文子串。采用动态规划解决即可。事件复杂度O（n^2).

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int maxlen = 0;
        String str = in.nextLine();
        char [] chs  = str.toCharArray();
        boolean dp[][] = new boolean[chs.length][chs.length];
        for(int right = 1;right<chs.length;++right){
            for(int left = right-1;left>=0;--left){
                if(chs[left] == chs[right]){
                    if(right-left<=2)dp[left][right] = true;
                    else dp[left][right] = dp[left+1][right-1];
                    if(dp[left][right])maxlen = Math.max(maxlen,right-left+1);
                }
            }
        }
        System.out.println(maxlen);
    }
}