题解 | #整数与IP地址间的转换#,还是废了一点时间

import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String s = sc.next();
            if (s.contains(".")) {
                System.out.println(ip2num(s));
            } else {
                System.out.println(num2ip(Long.parseLong(s)));
            }
        }
    }

    public static long ip2num(String ip) {
        String[] split = ip.split("\\.");
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < split.length; i++) {
            String binaryString = Integer.toBinaryString(Integer.parseInt(split[i]));
            for (int j = 0; j < 8 - binaryString.length(); j++) {
                builder.append("0");
            }
            builder.append(binaryString);
        }
        // 指定多少进制转换为10进制
        return Long.parseLong(builder.toString(),2);
    }

    public static String num2ip(long num){
        String binaryString = Long.toBinaryString(num);
        StringBuilder builder = new StringBuilder();
        for (int i = 0; i < 32 - binaryString.length(); i++) {
            builder.append("0");
        }
        builder.append(binaryString);
        String[] strings = new String[4];
        for (int i = 0; i < 4; i++) {
            String substring = builder.substring(i * 8, 8 * (i + 1));
            strings[i] = Integer.valueOf(substring,2) + "";
        }
        return String.join(".",strings);
    }
}