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);
        String ip = in.nextLine();
        String[] ipStr = ip.split("\\.");
        int[] ipCode = new int[4];
        int flag = 0;
        String element = "";
        if (ipStr.length != 4) {
            System.out.println("NO");
            flag = 1;
        } else if (!ip.matches("[0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+")) {
            System.out.println("NO");
            flag = 1;
        } else {
            for (int i = 0; i < 4; i++) {
                if (ipStr[i].isEmpty()) {
                    System.out.println("NO");
                    flag = 1;
                    break;
                } else {
                    ipCode[i] = Integer.parseInt(ipStr[i]);
                    element = ipStr[i];
                    if (ipCode[i] < 0 || ipCode[i] > 255 || (element.charAt(0) == '0' &&
                            ipCode[i] != 0)) {
                        System.out.println("NO");
                        flag = 1;
                        break;
                    }
                }
            }
        }
        if (flag == 0) {
            System.out.println("YES");
        }

    }
}