题解 | #合法IP#

import java.util.Arrays;
import java.util.Scanner;

// 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);
        // 注意 hasNext 和 hasNextLine 的区别
        String[] ipAddress = in.nextLine().split("\\.");
        //System.out.println(ipAddress[2].equals(""));
        //System.out.println(Arrays.toString(ipAddress));
        if (ipAddress.length != 4) {
            System.out.println("NO");
            return;
        } else {
            for (int i = 0 ; i < 4 ; ++i) {
                //System.out.println(ipAddress[i]);
                if (ipAddress[i].length() == 0) {
                    //System.out.println(i);
                    System.out.println("NO");

                    return;
                }
                //System.out.println(ipAddress[i]);
                for (int j = 0 ; j < ipAddress[i].length() ; ++j) {
                    //System.out.println(j);


                    if (ipAddress[i].length() > 1 && ipAddress[i].charAt(0) == '0') {
                        System.out.println("NO");
                        return;
                    }
                    if (!Character.isDigit(ipAddress[i].charAt(j))) {
                        System.out.println("NO");
                        return;
                    }
                    if (Integer.valueOf(ipAddress[i]) < 0 || Integer.valueOf(ipAddress[i]) > 255) {
                        System.out.println("NO");
                        return;
                    }

                }
            }
            System.out.println("YES");


        }
    }
}