题解 | #合法IP#

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
        // while (in.hasNextInt()) { // 注意 while 处理多个 case
        //     int a = in.nextInt();
        //     int b = in.nextInt();
        //     System.out.println(a + b);
        // }
        String ip = in.nextLine();
        String[] subs = ip.split("\\.");
        int len = subs.length;
        if (len != 4) {
            System.out.print("NO");
            return;
        }
        for (int i = 0; i < len; i++) {
            if (subs[i] == null || "".equals(subs[i])) {
                System.out.print("NO");
                return;
            }
            if (subs[i].length() > 1 && (subs[i].startsWith("0") || subs[i].startsWith("+"))) {
                System.out.print("NO");
                return;
            }
            try {
                int n = Integer.parseUnsignedInt(subs[i]);
                if (n > 255) {
                    System.out.print("NO");
                    return;
                }

            } catch (NumberFormatException e) {
                System.out.print("NO");
                return;
            }
        }
        System.out.print("YES");
    }
}