题解 | #合法IP#

import java.util.Scanner;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
 public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Pattern pattern = Pattern.compile("((\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])\\.){3}(\\d|[1-9]\\d|1\\d{2}|2[0-4]\\d|25[0-5])");
        Matcher mt;
        while (in.hasNext()) {
            String ipStr = in.nextLine();
            mt = pattern.matcher(ipStr);
            if (mt.matches()) {
                System.out.println("YES");
            } else {
                System.out.println("NO");
            }
        }
    }
}