题解 | #合法IP#

import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static final String regex = "\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}";

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String ip = sc.next();
        Matcher matcher = Pattern.compile(regex).matcher(ip);
        if (matcher.matches()) {
            String[] arr = ip.split("\\.");
            for (String s : arr) {
                if (s.length() > 1 && s.startsWith("0")) {
                    System.out.println("NO");
                    return;
                }
                int digit = Integer.parseInt(s);
                if (digit < 0 || digit > 255) {
                    System.out.println("NO");
                    return;
                }
            }
        } else {
            System.out.println("NO");
            return;
        }
        System.out.println("YES");
    }
}