题解 | #合法IP#正则

import java.util.*;
import java.util.stream.*;
import java.util.regex.*;
import java.util.function.*;

// 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);
        while (in.hasNextLine()) {
            String regexNum = "(25[0-5]|2[0-4]\\d|1\\d\\d|[1-9]\\d?|\\d)";
            System.out.println(
                in.nextLine()
                .matches(String.format("^(%s\\.){3}%s$", regexNum, regexNum))
                ? "YES" : "NO");
        }
    }
}