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.hasNext()) { // 注意 while 处理多个 case
            String s = in.nextLine();
            String res = "YES";
            String[] ip = s.split("\\.");
            if (ip.length != 4) {
                res = "NO";
            } else {
                for (int i = 0; i <= 3; i++) {
                    if (!ip[i].matches("[0-9]+") || 
                                (ip[i].charAt(0) == '0' && ip[i].length() >= 2) ||
                                    Integer.parseInt(ip[i]) < 0 || 
                                    Integer.parseInt(ip[i]) > 255) {
                        res = "NO";
                        break;
                    }
                }
            }
            System.out.println(res);
        }
    }
}